Mackie joined the Reds from QPR in the summer of 2013, but he failed to make a huge impact at the City Ground.
The attacker scored just only goals and created just 32 chances in 45 Championship appearances in the 2013-14 season.
The 29-year-old had a pass accuracy of 75% and a shot accuracy of 55%, and won 28 headers, 37 dribbles and 54 tackles.
The former Plymouth Argyle man was sent out on loan to Championship rivals Reading for the 2014-15 campaign.
Mackie scored five goals and created 24 chances in 32 league appearances for the Royals this past term.
The former Milton Keynes Dons attacker had a pass accuracy of 74% and a shot accuracy of 50%, and won 30 headers, 27 dribbles and 24 tackles.
Former QPR manager Redknapp believes that Mackie will prove to be a good signing for Rangers.
Jamie Mackie has gone back to QPR and it’s a good move. You know what you get with him and he’s a big fan favourite— Harry Redknapp (@Redknapp) June 17, 2015
Mackie is a hardworking player, and Rangers know exactly what they will get from him.
Under Chris Ramsey, QPR will be looking to bounce back to the Premier League following their relegation to the Championship at the end of the recently concluded 2014-15 season.
Having not made a huge impact at Forest, Mackie will have a point to prove in 2015-16, and Rangers fans will hope that the attacker turns on the style in his second spell at Loftus Road.