The director, who helmed the first two parts starring Chris Pratt, Zoe Saldana, Bradley Cooper, Vin Diesel and Dave Bautista, was fired by Marvel Studios' parent company Disney after his old, offensive tweets resurfaced on social media.
In the tweets, Gunn, 52, had cracked crude jokes dealing with pedophilia and rape.
The screenshots of the tweets, which ranged from 2009 through 2012, were shared by a conservative website The Daily Caller.
Gunn had penned the script for the threequel before he was sacked from the project.
"I am tremendously grateful to every person out there who has supported me over the past few months. I am always learning and will continue to work at being the best human being I can be," Gunn said.
"I deeply appreciate Disney's decision and I am excited to continue making films that investigate the ties of love that bind us all. I have been, and continue to be incredibly humbled by your love and support. From the bottom of my heart, thank you. Love to you all," he added.
Gunn's axing last year in July was followed with a backlash for Disney from both the fans and the cast of the film.
A petition, titled 'RE-HIRE JAMES GUNN' on website change.org was started by the fans and in the subsequent weeks it gained over tens of thousand signatures in Gunn's support.
The cast also came out with a statement in which they expressed shock over the company's decision. Bautista, who plays Drax the Destroyer in the series, was the most vocal supporter of the director.
On Saturday, Gunn's Marvel counterparts -- Peyton Reed ("Ant-Man") and Scott Derrickson ("Doctor Strange") -- congratulated the director on getting reinstated.
"Welcome back James," wrote Reed.
"What the hell?? I thought I was going to do it!!" he wrote.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)