I authored an easy twitter connect wordpress plugin which must display the 'logged in' user's title within the header after he logs in. The function is working correctly however i am not able to show the $user variable during my header or anywhere outdoors the function despite the fact that it's designated global.

This is actually the finish from the login function:

$user= $Twitter->get_accountVerify_credentials();
// show screen name (not real name)
$twitter_user = $user->screen_name;
// show profile image url
$twitter_image = $user->profile_image_url;

I can tell that it's effective since the $user will get printed, however when I refer to it as during my header.php file exactly the same way I'm able to a mistake: Notice: Undefined variable: user

Any suggestions?

Instead of getting ended within the scope from the variables, I'd write a function to obtain these details. Something similar to:

function get_twitter_user_name(){
    $user= $Twitter->get_accountVerify_credentials();
    return $user->screen_name;

Then, within the header, where I wish to display the title, I'd call the function like so:

<?php echo get_twitter_user_name(); ?>

With respect to the structure of the code, this might look quite different than I've here, but hopefully this provides you with one other way of dealing with this issue.