Needing just a draw to lift their 32nd championship trophy, Benfica started strongly in front of their own fans and were ahead within three minutes when when Cardozo pounced on a loose ball to volley in.
He could have added another moments later but arrived just too late to convert a David Luiz cross.
Rio Ave midfielder Wires was sent off on 10 minutes for dangerous play and Benfica created more chances, with Argentine forward Javier Saviola twice shooting just wide.
Rio Ave's Ricardo Chaves silenced a capacity crowd at the Luz Stadium with a headed equaliser on 70 minutes but Cardozo lifted spirits again eight minutes later, pouncing on another loose ball after a corner by Pablo Aimar.
The goal also earned Cardozo the top scorer's crown with 26 goals, one more than Porto's Colombian striker Radamel Falcao.
Braga, who went into the final day with a chance of winning the title if Benfica lost, drew 1-1 at Nacional.
Their second-place finish, five points adrift of Benfica on 71 points, was their best ever league performance and earned them a place in next season's Champions League third qualifying round.
Last season's champions Porto finished third and will enter the Europa League next season together with fourth-placed Sporting and fifth-placed Maritimo.
Belenenses and Leixoes were relegated.
