diff --git a/components/net/http_loader.rs b/components/net/http_loader.rs
index 3f9f9f46f0a..6574623232d 100644
--- a/components/net/http_loader.rs
+++ b/components/net/http_loader.rs
@@ -381,6 +381,12 @@ fn obtain_response(
     // TODO(#21261) connect_start: set if a persistent connection is *not* used and the last non-redirected
     // fetch passes the timing allow check
     let connect_start = precise_time_ms();
+    context
+        .timing
+        .lock()
+        .unwrap()
+        .set_attribute(ResourceAttribute::ConnectStart(connect_start));
+
     // https://url.spec.whatwg.org/#percent-encoded-bytes
     let request = HyperRequest::builder()
         .method(method)
diff --git a/components/net_traits/lib.rs b/components/net_traits/lib.rs
index 74234cd9c57..188857e5adb 100644
--- a/components/net_traits/lib.rs
+++ b/components/net_traits/lib.rs
@@ -452,7 +452,7 @@ pub struct ResourceFetchTiming {
     pub response_end: u64,
     pub redirect_start: u64,
     // pub redirect_end: u64,
-    // pub connect_start: u64,
+    pub connect_start: u64,
     pub connect_end: u64,
 }
 
@@ -468,6 +468,7 @@ pub enum ResourceAttribute {
     ResponseStart,
     RedirectStart(RedirectStartValue),
     FetchStart,
+    ConnectStart(u64),
     ConnectEnd(u64),
     ResponseEnd,
 }
@@ -489,6 +490,7 @@ impl ResourceFetchTiming {
             response_start: 0,
             fetch_start: 0,
             redirect_start: 0,
+            connect_start: 0,
             connect_end: 0,
             response_end: 0,
         }
@@ -510,6 +512,7 @@ impl ResourceFetchTiming {
                 },
             },
             ResourceAttribute::FetchStart => self.fetch_start = precise_time_ns(),
+            ResourceAttribute::ConnectStart(val) => self.connect_start = val,
             ResourceAttribute::ConnectEnd(val) => self.connect_end = val,
             ResourceAttribute::ResponseEnd => self.response_end = precise_time_ns(),
         }
diff --git a/components/script/dom/performanceresourcetiming.rs b/components/script/dom/performanceresourcetiming.rs
index 9726f2c04e4..0c7df4d4f80 100644
--- a/components/script/dom/performanceresourcetiming.rs
+++ b/components/script/dom/performanceresourcetiming.rs
@@ -120,7 +120,7 @@ impl PerformanceResourceTiming {
             fetch_start: resource_timing.fetch_start as f64,
             domain_lookup_start: 0.,
             domain_lookup_end: 0.,
-            connect_start: 0.,
+            connect_start: resource_timing.connect_start as f64,
             connect_end: resource_timing.connect_end as f64,
             secure_connection_start: 0.,
             request_start: resource_timing.request_start as f64,
@@ -192,6 +192,11 @@ impl PerformanceResourceTimingMethods for PerformanceResourceTiming {
         Finite::wrap(self.fetch_start)
     }
 
+    // https://w3c.github.io/resource-timing/#dom-performanceresourcetiming-connectstart
+    fn ConnectStart(&self) -> DOMHighResTimeStamp {
+        Finite::wrap(self.connect_start)
+    }
+
     // https://w3c.github.io/resource-timing/#dom-performanceresourcetiming-connectend
     fn ConnectEnd(&self) -> DOMHighResTimeStamp {
         Finite::wrap(self.connect_end)
diff --git a/components/script/dom/webidls/PerformanceResourceTiming.webidl b/components/script/dom/webidls/PerformanceResourceTiming.webidl
index 9fdd9c845da..1c9cf1bb8e5 100644
--- a/components/script/dom/webidls/PerformanceResourceTiming.webidl
+++ b/components/script/dom/webidls/PerformanceResourceTiming.webidl
@@ -17,7 +17,7 @@ interface PerformanceResourceTiming : PerformanceEntry {
     readonly attribute DOMHighResTimeStamp fetchStart;
     // readonly attribute DOMHighResTimeStamp domainLookupStart;
     // readonly attribute DOMHighResTimeStamp domainLookupEnd;
-    // readonly attribute DOMHighResTimeStamp connectStart;
+    readonly attribute DOMHighResTimeStamp connectStart;
     readonly attribute DOMHighResTimeStamp connectEnd;
     // readonly attribute DOMHighResTimeStamp secureConnectionStart;
     readonly attribute DOMHighResTimeStamp requestStart;