User Login Destination | to his first submission | Webforms
You can achieve using hook_user_login() function.

function mymodule_user_login(&amp;$edit, $account)
{
  // Your logic will set $redirection to the desired location.
  // Get the logic and fetch where do you want to redirect.
  // Here i am redirecting to node 34. You can fetch your own webform submission path
  // where do you want to redirect. 
  // Fetch the submission of done by the current users. by using http://api.drupalize.me/api/drupal/function/webform_get_submissions/7 function
  $redirection = 'node/34';


// Unless there is already a redirection going, or the user is trying to reset his password, we redirect to $redirection.
  if (empty($_GET['destination'])
    &amp;&amp; !is_null($redirection)
    &amp;&amp; (!isset($_POST['form_id']) || $_POST['form_id'] != 'user_pass_reset'))
  {
    $_GET['destination'] = $redirection; // Should we use $edit['redirect'] instead..?
  }
}