The Roosters became only the second club to win both the NRL and NRLW grand finals in one year, following Brisbane's double last year.
The women completed an undefeated season for their third title, while the men secured their 16th.
Thousands of supporters gathered at the SCG on Monday morning to welcome the champions after their celebrations began at the final whistle.
Both teams joined the 10am fan event, where NRLW coach John Strange praised the achievement.
"Outstanding result for the girls and obviously the boys getting the win as well," Strange said.
"Great for the club, first time ever, so I couldn't be prouder. "
Strange delighted fans with a worm dance, while NRL coach Trent Robinson celebrated with a boogie after remaining undefeated in four grand finals.
After the team song, players departed on a decorated open-air double-decker bus.
Captain and Clive Churchill medallist James Tedesco thanked supporters who backed the Roosters amid strong support for Newcastle.
"Big thanks for the way you've supported us all year, couldn't do it without you," Tedesco said.
The crowd's biggest cheers greeted Mark Nawaqanitawase, who scored twice in his final match before returning to rugby union after two seasons with the club.
Fans called for him to stay another year.