diff --git a/config/initializers/prometheus.rb b/config/initializers/prometheus.rb
index 4b842d841..7c2d42743 100644
--- a/config/initializers/prometheus.rb
+++ b/config/initializers/prometheus.rb
@@ -1,2 +1,4 @@
 require "govuk_app_config/govuk_prometheus_exporter"
-GovukPrometheusExporter.configure
+require "collectors/global_prometheus_collector"
+
+GovukPrometheusExporter.configure(collectors: [Collectors::GlobalPrometheusCollector])
diff --git a/lib/collectors/global_prometheus_collector.rb b/lib/collectors/global_prometheus_collector.rb
new file mode 100644
index 000000000..ff2f9065a
--- /dev/null
+++ b/lib/collectors/global_prometheus_collector.rb
@@ -0,0 +1,40 @@
+require "prometheus_exporter"
+require "prometheus_exporter/server"
+
+# Load Rails models as not automatically included for Prometheus Exporter
+require File.expand_path("../../config/environment", __dir__) unless defined? Rails
+
+module Collectors
+  class GlobalPrometheusCollector < PrometheusExporter::Server::TypeCollector
+    def type
+      "signon_global"
+    end
+
+    def metrics
+      token_expiry_timestamp = PrometheusExporter::Metric::Gauge.new("signon_api_user_token_expiry_timestamp_seconds", "Timestamp when API User token expires")
+
+      token_expiry_info.each do |token|
+        token_expiry_timestamp.observe(token[:expires_at], api_user: token[:api_user], application: token[:application_name])
+      end
+
+      [token_expiry_timestamp]
+    end
+
+  private
+
+    def token_expiry_info
+      # Cache metric to prevent needless expensive calls to the database
+      Rails.cache.fetch("token_expiry_info", expires_in: 1.hour) do
+        ApiUser.all.flat_map do |user|
+          user.authorisations.where(revoked_at: nil).map do |token|
+            {
+              expires_at: token.expires_at.to_i,
+              api_user: user.email,
+              application_name: token.application.name.parameterize,
+            }
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/lib/collectors/global_prometheus_collector_test.rb b/test/lib/collectors/global_prometheus_collector_test.rb
new file mode 100644
index 000000000..d53a0282e
--- /dev/null
+++ b/test/lib/collectors/global_prometheus_collector_test.rb
@@ -0,0 +1,27 @@
+require "test_helper"
+
+class GlobalPrometheusCollectorTest < ActiveSupport::TestCase
+  def setup
+    @collector = Collectors::GlobalPrometheusCollector.new
+    @api_user = api_user_with_token("user1", token_count: 3)
+  end
+
+  context "#metrics" do
+    should "list all non-revoked token expiry timestamps" do
+      @api_user.authorisations[2].revoke
+
+      metrics = @collector.metrics
+
+      assert_equal metrics.first.data, {
+        {
+          api_user: @api_user.email,
+          application: @api_user.authorisations.first.application.name.parameterize,
+        } => @api_user.authorisations.first.expires_at.to_i,
+        {
+          api_user: @api_user.email,
+          application: @api_user.authorisations.second.application.name.parameterize,
+        } => @api_user.authorisations.second.expires_at.to_i,
+      }
+    end
+  end
+end