Goals from Sadio Mané and Kingsley Coman put Al-Nassr in control before Damac pulled one back before the hour. Ronaldo then scored from a free-kick to restore the two-goal advantage and added a second in the closing stages, taking his career tally to 974 goals as he continues to pursue the milestone of 1,000.
Head coach Jorge Jesus substituted him late on and the cameras caught the 41-year-old in tears on the bench as the full-time whistle confirmed the title.
The wait had been extended by a series of near-misses so painful as to seem almost scripted. Five days before the final-day win, Al-Nassr were seconds away from the title when goalkeeper Bento allowed a long throw-in to squirm into the net in stoppage time, gifting Al-Hilal a 1-1 draw and leaving the two clubs level with one game remaining.
The weekend before that, Ronaldo had refused to collect his runners-up medal after Al-Nassr lost the AFC Champions League Two final 1-0 to Gamba Osaka in front of their own supporters.
The title is the eighth league championship of Ronaldo's career and his first in Saudi Arabia after three seasons of near-misses. His only other honour at the club was the 2023 Arab Club Champions Cup, a competition widely viewed as exhibition-level.
Jesus, 71, who is expected to leave the club when his contract expires next month, reflected on the achievement of a coach who arrived in a situation that required immediate results.
"We didn't get what we wanted in the Cup but there is one more final for us — the Saudi Pro League title, which is very important to us."
Ronaldo is under contract with Al-Nassr until 2027 having signed a new lucrative two-year deal last summer. He spoke last month about the trajectory of his career with characteristic directness.
"The end of my career is getting closer. Let's enjoy every game. I keep playing not only for this generation, but also for the previous one and the one coming next."