diff --git a/app/assets/stylesheets/pages/projects.scss b/app/assets/stylesheets/pages/projects.scss
index 8e53876eb4f..bcb306d97d5 100644
--- a/app/assets/stylesheets/pages/projects.scss
+++ b/app/assets/stylesheets/pages/projects.scss
@@ -18,12 +18,9 @@
   }
 
   .input-group {
-    display: flex;
-
     .select2-container {
       display: unset;
       max-width: unset;
-      width: unset !important;
       flex-grow: 1;
     }
 
diff --git a/app/views/projects/_new_project_fields.html.haml b/app/views/projects/_new_project_fields.html.haml
index 276363df7da..5129f11875c 100644
--- a/app/views/projects/_new_project_fields.html.haml
+++ b/app/views/projects/_new_project_fields.html.haml
@@ -12,9 +12,9 @@
   .form-group.project-path.col-sm-6
     = f.label :namespace_id, class: 'label-bold' do
       %span= s_("Project URL")
-    .input-group
+    .input-group.flex-nowrap
       - if current_user.can_select_namespace?
-        .input-group-prepend.has-tooltip{ title: root_url }
+        .input-group-prepend.flex-shrink-0.has-tooltip{ title: root_url }
           .input-group-text
             = root_url
         - namespace_id = namespace_id_from(params)
@@ -23,10 +23,10 @@
                                       display_path: true,
                                       extra_group: namespace_id),
                    {},
-                   { class: 'select2 js-select-namespace qa-project-namespace-select', tabindex: 1, data: { track_label: "#{track_label}", track_event: "activate_form_input", track_property: "project_path", track_value: "" }})
+                   { class: 'select2 js-select-namespace qa-project-namespace-select block-truncated', tabindex: 1, data: { track_label: "#{track_label}", track_event: "activate_form_input", track_property: "project_path", track_value: "" }})
 
       - else
-        .input-group-prepend.static-namespace.has-tooltip{ title: user_url(current_user.username) + '/' }
+        .input-group-prepend.static-namespace.flex-shrink-0.has-tooltip{ title: user_url(current_user.username) + '/' }
           .input-group-text.border-0
             #{user_url(current_user.username)}/
         = f.hidden_field :namespace_id, value: current_user.namespace_id
diff --git a/changelogs/unreleased/59189-long-names-in-project-path-namespace-dropdown-breaks-past-container.yml b/changelogs/unreleased/59189-long-names-in-project-path-namespace-dropdown-breaks-past-container.yml
new file mode 100644
index 00000000000..bed7fcf2651
--- /dev/null
+++ b/changelogs/unreleased/59189-long-names-in-project-path-namespace-dropdown-breaks-past-container.yml
@@ -0,0 +1,5 @@
+---
+title: Prevent namespace dropdown in new project form from exceeding container
+merge_request: 26343
+author:
+type: fixed