Thomas Flynn got the crucial goal at McHale Park
Galway have ended Mayo's hopes of a sixth Connacht championship in a row.
The Tribesmen defeated their rivals 1-12 to 0-12 to book their place in a final against Roscommon, who beat Sligo last weekend.
Thomas Flynn's goal on 54 minutes swung the game in Galway's direction to make the scores 0-11 to 1-8 at that point before Paul Conroy and Danny Cummins added two more points in quick succession.
Pat Lam has done such a great job with the Galway footballers. To think they were almost disbanded a few years back #Galway_GAA— Oisin Langan (@oisinlangan) June 18, 2016
Mayo failed to score in a 20 minute stretch in the second half as Galway got their first championship win over their neighbours for almost a decade.
Galway's last appearance in the Connacht final was back in 2014 when they were comfortably beaten by Mayo.
Mayo's Kevin Keane tackled by Gary Sice and Shane Walsh of Galway ©INPHO/Lorraine O'Sullivan
Mayo's Stephen Coen celebrates after scoring a point ©INPHO/Lorraine O'Sullivan
Mayo's Seamus O'Se and Declan Kyne of Galway ©INPHO/Lorraine O'Sullivan
Mayo's Keith Higgins and Gareth Bradshaw of Galway ©INPHO/Lorraine O'Sullivan