Perform action once a form has been validated
You should add a submit callback instead of a validation callback. Submit callbacks are called after the form has been validated.

function yourmodule_form_FORM_ID_alter(&amp;$form, &amp;$form_state) {
  $form['#submit'][] = 'yourmodule_custom_submit_callback';
}

function yourmodule_custom_submit_callback($form, &amp;$form_state) {
  // Execute here your code
}