Pittodrie boss Mark McGhee had been chasing MacLean all January but it was the sale of Lee Miller to Middlesbrough earlier on Monday evening that freed up the funds for him to land the 27-year-old.
MacLean joined Argyle in 2008 after a spell at Cardiff.
Having started his career at Rangers, he also enjoyed spells at Scunthorpe and Sheffield Wednesday.
Paterson, who can operate at left-back or left midfield, played more than 100 games for Dundee United and Motherwell before moving south in 2008.
Both players go straight in to the squad for tomorrow night's Clydesdale Bank Premier League game with Falkirk.
Source: Team Talk
Source: Team Talk