The experienced centre back has penned a two-year deal at Pittodrie after his short contract in Dingwall came to an end.
29-year-old Quinn came through the youth ranks at Motherwell before moving to Cardiff in 2009, then signing for Doncaster Rovers where he made over 70 appearances before returning to Scotland last year.
Quinn told the official AFC website: "Aberdeen is huge club and I can't wait to get started. When I heard Derek McInnes was interested in signing me, it was something of a no-brainer while playing in Europe was another major factor."
Dons gaffer Derek McInnes added: "I'm delighted to sign Paul, who has been a major influence on Ross County's form in the second half of the season. We're looking forward to him having a positive influence on our team.
"We've watched Paul on several occasions in the last few months and the key qualities he'll bring to the team are his experience, leadership and competitiveness. You cannot have too many leaders on the pitch."