In a drama-filled grand final that included a biting allegation and bunker controversy, Penrith pulled away late in front of a crowd of 80,156 people at Accor Stadium on Sunday night.
The win makes them only the third team in history to claim four straight premierships and the first since the great St George side won 11 in a row from 1956 to 1966.
It came as the result threatened to be overshadowed by claims Melbourne star Cameron Munster had bitten Paul Alamoti's arm late in the second half.
Munster denied the claim but was put on report by referee Ashley Klein, who said he could not be certain what had happened.
Melbourne were also denied a crucial try by the bunker at 10-6 down in the 50th minute when centre Jack Howarth crashed over.
Initial replays appeared to show he grounded the ball, but the NRL provided media evidence afterwards that he was held up by Dylan Edwards and Izack Tago.
Still, the story from the night was Penrith's fourth straight title.
Penrith players sported all four premiership rings after the game, after triumphs over South Sydney, Parramatta and Brisbane since 2021.
"I'm just looking at some of the boys with four rings on their hands, like, how did this happen?" coach Ivan Cleary said.
"It just sort of feels like it validates everything that we've done and we've tried to become tonight. I couldn't be more proud."
