Ronaldo, who missed his team's 4-1 derby defeat to Manchester City on Sunday with an injury, opened the scoring for the hosts in the 12th minute, curling an effort from well outside the penalty area past Hugo Lloris' far post to give United the early lead.
Tottenham had some quality moments following the Ronaldo opener, seeing a Ben Davies strike after some nice team play ruled out for offside and forcing Diogo Dalot to head away another Spurs effort off his on goal line.
The visitors' efforts were rewarded shortly after the half-hour mark when Alex Telles was whistled for handball in the penalty area and Harry Kane stepped up and calmly beat David De Gea from the spot to make it 1-1.
United retook the lead ahead of the break with a second from Ronaldo, who smashed home a first-time shot from Jadon Sancho's lovely pass across the six-yard box in a quick-hitting counter-attack from Ralf Rangnick's side.
The two first-half goals from Ronaldo were his 805th and 806th, passing Josef Bican for the most in competitive matches, according to RSSSF.
A Harry Maguire own goal got Antonio Conte's Spurs back on level terms as the second half wore on, with De Gea only able to watch as the England international redirected Sergio Reguilon's cross past him from close range.
However, Ronaldo wasn't done with his heroics on the night, outjumping Tottenham's defenders from a corner kick and powering a header into the top corner to give United the lead and all three points to stay precariously in the top four of the Premier League.
"Everybody knows Cristiano -- there's no need to talk about him," said Paul Pogba after the match. "That's what he does. He didn't play in the last game, but he comes back and scores three goals. Everybody's happy.
"Ronaldo was brilliant. I think that's all we needed -- a reaction. We scored beautiful goals. Even when we conceded a goal, we came back and scored again. The mentality was there again today."
It was the 37-year-old Ronaldo's 59th career hat trick, with the third putting him up to 807 goals in competitive matches during his illustrious career.
The result puts Man United in fourth place in the table on 50 points from 29 matches, two ahead of fifth-placed Arsenal, who have a whopping four games in hand.
The missed points for Tottenham leave them in seventh place, picking up 45 points from 27 games played.