How to override Page Title of View using Contextual Filter
In Drupal 8, if you are using a contextual filter to pass a taxonomy term to a View and want to change the page title to match with the term title, you can:

/**
 * Implements hook_preprocess_views_view().
 */
function HOOK_preprocess_views_view(&amp;$variables) {

  $id = $variables['id'];

  if( $id == 'YOUR_VIEW_NAME' &amp;&amp; $variables['view']-&gt;args[0]) {

    // Get tid from contextual argument of the view
    $tid = $variables['view']-&gt;args[0];

    // Load the Term Entity
    $term = Term::load($tid);

    // Term Title
    $new_title = $term-&gt;getName();

    // Set the new Page Title
    $request = \Drupal::request();
    if ($route = $request-&gt;attributes-&gt;get(\Symfony\Cmf\Component\Routing\RouteObjectInterface::ROUTE_OBJECT)) {
      $route-&gt;setDefault('_title', $new_title);
    }
  }
}