The Belgian netted his first goal for the club that he joined 13 months ago to cancel out Stephane Sessegnon's first-half opener at The Hawthorns.
Daley Blind had to stroke home an 87th-minute equaliser to salvage a point for United but, despite admitting that the result was disappointing, Fellaini is happy to get off the mark.
"My first goal this season and for Manchester United as well," he told Sky Sports News. "It was a great feeling.
"I have waited a long time for this moment. I hope I can score some more goals for us this season. It was good for me but the result is a disappointment."
Tonight's draw lifted United above Arsenal into sixth in the Premier League table.