Greencastle are Inishowen League Jackie Crossan Premier Division Champions for the first time in the club's history.
The Chapel Road side secured the title by way of Glengad United's 1-1 draw with Carn on Tuesday evening.
Glengad, winners the last four years needed to win all their matches to stay in the title hunt but a late equaliser from Carn's Conor Doherty means the title goes to Greencastle who still have two games to play.
The league crown comes just days after Pat McLaughlin's men won the Ulster Junior Cup while they also lifted this season's league cup
It was a mixed evening for Greencastle on Tuesday who lost 2-0 to Bonagee United in the semi final of the Knockalla Caravans Cup at the Dry Arch Park.
Jordan Armstrong and Ryan Rainey scored the goals with Bonagee awaiting the winners of Glengad and Kildrum in the Final.