Integrate Membership with MailChimp API

Membership + MailChimp.php

add_action('register_user','mailchimp_add_to_list')

function mailchimp_add_to_list ($user_id)

{

// Get Full Name and Email from BuddyPress
	$name = bp_core_get_user_displayname( $user_id );
	$email = bp_core_get_user_email($user_id);

$fullname = explode(" ",$name);
$fname = $fullname[0];
$lname = $fullname[1];

// Settings for this subscriber
	$double_optin=true;
	$update_existing=false;
	$replace_interests=true;
	$send_welcome=false;
	$email_type = 'html';

// Name of the Subscriber added here
	$merges = array('FNAME'=>$fname, 'LNAME'=>$lname);

// Data Array that gets sent to MailChimp
// IMPORTANT :  Put API Key + List ID in this array
	$data = array(
        'email_address'=>$email,
        'apikey'=>$apikey, // Put API Key here
        'merge_vars' => $merges,
        'id' => $listId, // Put List ID Here or remove this line if you don't have one
        'double_optin' => $double_optin,
        'update_existing' => $update_existing,
        'replace_interests' => $replace_interests,
        'send_welcome' => $send_welcome,
        'email_type' => $email_type
    );

// JSON over XML-RPC because its lightweight adnd fast
	$payload = json_encode($data);

// The url to send this to, Im taking that your data center is us7 based on your thread
	$submit_url = "http://us7.api.mailchimp.com/1.3/?method=listSubscribe";

// cURL to send the data over
	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL, $submit_url);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
	curl_setopt($ch, CURLOPT_POST, true);
	curl_setopt($ch, CURLOPT_POSTFIELDS, urlencode($payload));

// Get the response and process it
	$result = curl_exec($ch);
	curl_close ($ch);

	$response = json_decode($result);

	// This bit is optional
		if ($response->error){
		    // Put a success message or callback code here (Optional)
		} else {
		        // If the add user operation fails, put the callback code here (Optional)
		}

}

Copy Paste in functions.php or Site specific plugin and new members automatically get added to specified List