David de Gea was called into action on numerous occasions to save United as bottom of the Premier League table side Norwich held their own.
Ronaldo saw a shot beaten away by Tim Krul in the 37th minute and the home goalkeeper also tipped over a Harry Maguire header on the stroke of halftime after Alex Telles hit the bar with a deflected free kick early on.
The Portugal international made no mistake with the spot-kick, smashing it into the left-hand corner.
There was some concern for Victor Lindelof during the match when he went down pointing to his chest a few minutes beforehand. However, he was able to walk off the pitch unassisted.
The result lifted United to fifth place in the standings on 27 points from 16 games, behind fourth-placed West Ham United on goal difference, while Norwich stayed bottom on 10 points.
Information from Reuters contributed to this report.