diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ad5d7cf9..f532c5dce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,16 @@
 ## Unreleased
 
 - Support global file-level tags in metrics.yaml ([bug 1745283](https://bugzilla.mozilla.org/show_bug.cgi?id=1745283))
+- Automatically generate a build date when generating build info ([#431](https://github.com/mozilla/glean_parser/pull/431)).
+  Enabled for Kotlin and Swift.
+  This can be changed with the `build_date` command line option.
+  `build_date=0` will use a static unix epoch time.
+  `build_date=2022-01-03T17:30:00` will parse the ISO8601 string to use (as a UTC timestamp).
+  Other values will throw an error.
+
+  Example:
+
+    glean_parser translate --format kotlin --option build_date=2021-11-01T01:00:00 path/to/metrics.yaml
 
 ## 4.3.1
 
diff --git a/glean_parser/kotlin.py b/glean_parser/kotlin.py
index c9a5e32a9..edfda12f2 100644
--- a/glean_parser/kotlin.py
+++ b/glean_parser/kotlin.py
@@ -132,6 +132,29 @@ def class_name(obj_type: str) -> str:
     return util.Camelize(obj_type) + "MetricType"
 
 
+def generate_build_date(date: Optional[str]) -> str:
+    """
+    Generate the build timestamp.
+    """
+
+    ts = util.build_date(date)
+
+    data = [
+        str(ts.year),
+        # In Java the first month of the year in calendars is JANUARY which is 0.
+        # In Python it's 1-based
+        str(ts.month - 1),
+        str(ts.day),
+        str(ts.hour),
+        str(ts.minute),
+        str(ts.second),
+    ]
+    components = ", ".join(data)
+
+    # DatetimeMetricType takes a `Calendar` instance.
+    return f'Calendar.getInstance(TimeZone.getTimeZone("GMT+0")).also {{ cal -> cal.set({components}) }}'  # noqa
+
+
 def output_gecko_lookup(
     objs: metrics.ObjectTree, output_dir: Path, options: Optional[Dict[str, Any]] = None
 ) -> None:
@@ -249,6 +272,11 @@ def output_kotlin(
         - `with_buildinfo`: If "true" a `GleanBuildInfo.kt` file is generated.
           Otherwise generation of that file is skipped.
           Defaults to "true".
+        - `build_date`: If set to `0` a static unix epoch time will be used.
+                        If set to a ISO8601 datetime string (e.g. `2022-01-03T17:30:00`)
+                        it will use that date.
+                        Other values will throw an error.
+                        If not set it will use the current date & time.
     """
     if options is None:
         options = {}
@@ -257,6 +285,7 @@ def output_kotlin(
     glean_namespace = options.get("glean_namespace", "mozilla.components.service.glean")
     namespace_package = namespace[: namespace.rfind(".")]
     with_buildinfo = options.get("with_buildinfo", "true").lower() == "true"
+    build_date = options.get("build_date", None)
 
     # Write out the special "build info" object
     template = util.get_jinja2_template(
@@ -264,6 +293,7 @@ def output_kotlin(
     )
 
     if with_buildinfo:
+        build_date = generate_build_date(build_date)
         # This filename needs to start with "Glean" so it can never clash with a
         # metric category
         with (output_dir / "GleanBuildInfo.kt").open("w", encoding="utf-8") as fd:
@@ -272,6 +302,7 @@ def output_kotlin(
                     namespace=namespace,
                     namespace_package=namespace_package,
                     glean_namespace=glean_namespace,
+                    build_date=build_date,
                 )
             )
             fd.write("\n")
diff --git a/glean_parser/swift.py b/glean_parser/swift.py
index 7dcc65ea8..712e6d947 100644
--- a/glean_parser/swift.py
+++ b/glean_parser/swift.py
@@ -134,6 +134,33 @@ def variable_name(var: str) -> str:
         return var
 
 
+class BuildInfo:
+    def __init__(self, build_date):
+        self.build_date = build_date
+
+
+def generate_build_date(date: Optional[str]) -> str:
+    """
+    Generate the build timestamp.
+    """
+
+    ts = util.build_date(date)
+
+    data = [
+        ("year", ts.year),
+        ("month", ts.month),
+        ("day", ts.day),
+        ("hour", ts.hour),
+        ("minute", ts.minute),
+        ("second", ts.second),
+    ]
+
+    # The internal DatetimeMetricType API can take a `DateComponents` object,
+    # which lets us easily specify the timezone.
+    components = ", ".join([f"{name}: {val}" for (name, val) in data])
+    return f'DateComponents(calendar: Calendar.current, timeZone: TimeZone(abbreviation: "UTC"), {components})'  # noqa
+
+
 class Category:
     """
     Data struct holding information about a metric to be used in the template.
@@ -157,6 +184,14 @@ def output_swift(
         - namespace: The namespace to generate metrics in
         - glean_namespace: The namespace to import Glean from
         - allow_reserved: When True, this is a Glean-internal build
+        - with_buildinfo: If "true" the `GleanBuildInfo` is generated.
+          Otherwise generation of that file is skipped.
+          Defaults to "true".
+        - build_date: If set to `0` a static unix epoch time will be used.
+                      If set to a ISO8601 datetime string (e.g. `2022-01-03T17:30:00`)
+                      it will use that date.
+                      Other values will throw an error.
+                      If not set it will use the current date & time.
     """
     if options is None:
         options = {}
@@ -174,6 +209,12 @@ def output_swift(
 
     namespace = options.get("namespace", "GleanMetrics")
     glean_namespace = options.get("glean_namespace", "Glean")
+    with_buildinfo = options.get("with_buildinfo", "true").lower() == "true"
+    build_date = options.get("build_date", None)
+    build_info = None
+    if with_buildinfo:
+        build_date = generate_build_date(build_date)
+        build_info = BuildInfo(build_date=build_date)
 
     filename = "Metrics.swift"
     filepath = output_dir / filename
@@ -199,6 +240,7 @@ def output_swift(
                 namespace=namespace,
                 glean_namespace=glean_namespace,
                 allow_reserved=options.get("allow_reserved", False),
+                build_info=build_info,
             )
         )
         # Jinja2 squashes the final newline, so we explicitly add it
diff --git a/glean_parser/templates/kotlin.buildinfo.jinja2 b/glean_parser/templates/kotlin.buildinfo.jinja2
index 22b795644..2f86b90e1 100644
--- a/glean_parser/templates/kotlin.buildinfo.jinja2
+++ b/glean_parser/templates/kotlin.buildinfo.jinja2
@@ -14,14 +14,18 @@ Jinja2 template is not. Please file bugs! #}
 
 package {{ namespace }}
 
+import java.util.Calendar
+import java.util.TimeZone
 import {{ glean_namespace }}.BuildInfo
 import {{ namespace_package }}.BuildConfig
 
+@Suppress("MagicNumber")
 internal object GleanBuildInfo {
     val buildInfo: BuildInfo by lazy {
         BuildInfo(
             versionCode = BuildConfig.VERSION_CODE.toString(),
-            versionName = BuildConfig.VERSION_NAME
+            versionName = BuildConfig.VERSION_NAME,
+            buildDate = {{ build_date }}
         )
     }
 }
diff --git a/glean_parser/templates/swift.jinja2 b/glean_parser/templates/swift.jinja2
index 7d0c14efe..2d9c87660 100644
--- a/glean_parser/templates/swift.jinja2
+++ b/glean_parser/templates/swift.jinja2
@@ -60,6 +60,16 @@ import {{ glean_namespace }}
 // swiftlint:disable force_try
 
 extension {{ namespace }} {
+    {% if build_info %}
+    class GleanBuild {
+        private init() {
+            // Intentionally left private, no external user can instantiate a new global object.
+        }
+
+        public static let info = BuildInfo(buildDate: {{ build_info.build_date }})
+    }
+    {% endif %}
+
     {% for category in categories %}
     {% if category.contains_pings %}
     class {{ category.name|Camelize }} {
diff --git a/glean_parser/util.py b/glean_parser/util.py
index 9b631e17b..f12fdd75c 100644
--- a/glean_parser/util.py
+++ b/glean_parser/util.py
@@ -24,6 +24,26 @@
 if sys.version_info < (3, 7):
     import iso8601  # type: ignore
 
+    def date_fromisoformat(datestr: str) -> datetime.date:
+        try:
+            return iso8601.parse_date(datestr).date()
+        except iso8601.ParseError:
+            raise ValueError()
+
+    def datetime_fromisoformat(datestr: str) -> datetime.datetime:
+        try:
+            return iso8601.parse_date(datestr)
+        except iso8601.ParseError:
+            raise ValueError()
+
+else:
+
+    def date_fromisoformat(datestr: str) -> datetime.date:
+        return datetime.date.fromisoformat(datestr)
+
+    def datetime_fromisoformat(datestr: str) -> datetime.datetime:
+        return datetime.datetime.fromisoformat(datestr)
+
 
 TESTING_MODE = "pytest" in sys.modules
 
@@ -360,13 +380,7 @@ def parse_expires(expires: str) -> datetime.date:
     Raises a ValueError in case the string is not properly formatted.
     """
     try:
-        if sys.version_info < (3, 7):
-            try:
-                return iso8601.parse_date(expires).date()
-            except iso8601.ParseError:
-                raise ValueError()
-        else:
-            return datetime.date.fromisoformat(expires)
+        return date_fromisoformat(expires)
     except ValueError:
         raise ValueError(
             f"Invalid expiration date '{expires}'. "
@@ -407,6 +421,31 @@ def validate_expires(expires: str) -> None:
         )
 
 
+def build_date(date: Optional[str]) -> datetime.datetime:
+    """
+    Generate the build timestamp.
+
+    If `date` is set to `0` a static unix epoch time will be used.
+    If `date` it is set to a ISO8601 datetime string (e.g. `2022-01-03T17:30:00`)
+    it will use that date.
+    Note that any timezone offset will be ignored and UTC will be used.
+    Otherwise it will throw an error.
+
+    If `date` is `None` it will use the current date & time.
+    """
+
+    if date is not None:
+        date = str(date)
+        if date == "0":
+            ts = datetime.datetime(1970, 1, 1, 0, 0, 0)
+        else:
+            ts = datetime_fromisoformat(date).replace(tzinfo=datetime.timezone.utc)
+    else:
+        ts = datetime.datetime.utcnow()
+
+    return ts
+
+
 def report_validation_errors(all_objects):
     """
     Report any validation errors found to the console.
diff --git a/tests/test_cli.py b/tests/test_cli.py
index a85db513d..edee4c9be 100755
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -96,6 +96,84 @@ def test_translate_no_buildinfo(tmpdir):
         assert "package Foo" in content
 
 
+def test_translate_build_date(tmpdir):
+    """Test with a custom build date."""
+    runner = CliRunner()
+    result = runner.invoke(
+        __main__.main,
+        [
+            "translate",
+            str(ROOT / "data" / "core.yaml"),
+            "-o",
+            str(tmpdir),
+            "-f",
+            "kotlin",
+            "-s",
+            "namespace=Foo",
+            "-s",
+            "build_date=2020-01-01T17:30:00",
+            "--allow-reserved",
+        ],
+    )
+    assert result.exit_code == 0
+
+    path = Path(str(tmpdir)) / "GleanBuildInfo.kt"
+    with path.open(encoding="utf-8") as fd:
+        content = fd.read()
+    assert "buildDate = Calendar.getInstance" in content
+    assert "cal.set(2020, 0, 1, 17, 30" in content
+
+
+def test_translate_fixed_build_date(tmpdir):
+    """Test with a custom build date."""
+    runner = CliRunner()
+    result = runner.invoke(
+        __main__.main,
+        [
+            "translate",
+            str(ROOT / "data" / "core.yaml"),
+            "-o",
+            str(tmpdir),
+            "-f",
+            "kotlin",
+            "-s",
+            "namespace=Foo",
+            "-s",
+            "build_date=0",
+            "--allow-reserved",
+        ],
+    )
+    assert result.exit_code == 0
+
+    path = Path(str(tmpdir)) / "GleanBuildInfo.kt"
+    with path.open(encoding="utf-8") as fd:
+        content = fd.read()
+    assert "buildDate = Calendar.getInstance" in content
+    assert "cal.set(1970" in content
+
+
+def test_translate_borked_build_date(tmpdir):
+    """Test with a custom build date."""
+    runner = CliRunner()
+    result = runner.invoke(
+        __main__.main,
+        [
+            "translate",
+            str(ROOT / "data" / "core.yaml"),
+            "-o",
+            str(tmpdir),
+            "-f",
+            "kotlin",
+            "-s",
+            "namespace=Foo",
+            "-s",
+            "build_date=1",
+            "--allow-reserved",
+        ],
+    )
+    assert result.exit_code == 1
+
+
 def test_translate_errors(tmpdir):
     """Test the 'translate' command."""
     runner = CliRunner()
diff --git a/tests/test_kotlin.py b/tests/test_kotlin.py
index 86bbdcc1a..31a2d71b6 100644
--- a/tests/test_kotlin.py
+++ b/tests/test_kotlin.py
@@ -88,6 +88,10 @@ def test_parser(tmpdir):
         content = fd.read()
         assert 'category = ""' in content
 
+    with (tmpdir / "GleanBuildInfo.kt").open("r", encoding="utf-8") as fd:
+        content = fd.read()
+        assert "buildDate = Calendar.getInstance" in content
+
     run_linters(tmpdir.glob("*.kt"))
 
 
diff --git a/tests/test_swift.py b/tests/test_swift.py
index f52979225..7dcac08c5 100644
--- a/tests/test_swift.py
+++ b/tests/test_swift.py
@@ -49,6 +49,56 @@ def test_parser(tmpdir):
         assert "True if the user has set Firefox as the default browser." in content
         assert "جمع 搜集" in content
         assert 'category: ""' in content
+        assert "class GleanBuild" in content
+        assert "BuildInfo(buildDate:" in content
+
+    run_linters(tmpdir.glob("*.swift"))
+
+
+def test_parser_no_build_info(tmpdir):
+    """Test translating metrics to Swift files without build info."""
+    tmpdir = Path(str(tmpdir))
+
+    translate.translate(
+        ROOT / "data" / "core.yaml",
+        "swift",
+        tmpdir,
+        {"with_buildinfo": "false"},
+        {"allow_reserved": True},
+    )
+
+    assert set(x.name for x in tmpdir.iterdir()) == set(["Metrics.swift"])
+
+    # Make sure descriptions made it in
+    with (tmpdir / "Metrics.swift").open("r", encoding="utf-8") as fd:
+        content = fd.read()
+
+        assert "class GleanBuild" not in content
+
+    run_linters(tmpdir.glob("*.swift"))
+
+
+def test_parser_custom_build_date(tmpdir):
+    """Test translating metrics to Swift files without build info."""
+    tmpdir = Path(str(tmpdir))
+
+    translate.translate(
+        ROOT / "data" / "core.yaml",
+        "swift",
+        tmpdir,
+        {"build_date": "2020-01-01T17:30:00"},
+        {"allow_reserved": True},
+    )
+
+    assert set(x.name for x in tmpdir.iterdir()) == set(["Metrics.swift"])
+
+    # Make sure descriptions made it in
+    with (tmpdir / "Metrics.swift").open("r", encoding="utf-8") as fd:
+        content = fd.read()
+
+        assert "class GleanBuild" in content
+        assert "BuildInfo(buildDate:" in content
+        assert "year: 2020, month: 1, day: 1" in content
 
     run_linters(tmpdir.glob("*.swift"))