Gunn was set to work on the upcoming third instalment in the franchise but Disney severed ties with him after messages in which he joked about subjects including paedophilia and rape, which he posted more than 10 years ago, emerged.
In one tweet he wrote, "I like when little boys touch me in my silly place."
In another: "The best thing about being raped is when you're done being raped and it’s like ‘whew this feels great, not being raped!'"
Although Gunn had never formally been confirmed as the director of the third film, set to come out in 2020, Disney reacted swiftly to the discovery of Gunn’s tweets, which had been written between 2008 and 2011.
Walt Disney Studios chairman Alan Horn said that the tweets were indefensible.
On Monday, a statement signed by the cast, also including Karen Gillan, Dave Bautista, Michael Rooker, Pom Klementieff and the director's brother Sean Gunn, was shared on Instagram.
It says: "We fully support James Gunn. We were all shocked by his abrupt firing last week and have intentionally waited these 10 days to respond in order to think, pray, listen and discuss.
"In that time, we've been encouraged by the outpouring of support from fans and members of the media who wish to see James reinstated as director of Volume 3 as well as discouraged by those so easily duped into believing the many outlandish conspiracy theories surrounding him."
The statement continues: "Being in the Guardians Of The Galaxy movies has been a great honour in each of our lives.
"We cannot let this moment pass without expressing our love, support, and gratitude for James.
"We are not here to defend his jokes of many years ago but rather to share our experience having spend many years together on set making Guardians Of The Galaxy 1 and 2.
"The character he has shown in the wake of his firing is consistent with the man he was every day on set, and his apology, now and from years ago when first addressing these remarks, we believe is from the heart, a heart we all know, trust, and love.
"In casting each of us to help him tell the story of misfits who find redemption, he changed our lives forever. We believe the theme of redemption has never been more relevant than now."
It continues: "Each of us looks forward to working with our friend James again in the future. His story isn't over - not by a long shot.
"There is little due process in the court of public opinion. James is likely not the last good person to be put on trial.
"Given the growing political divide in this country, it's safe to say instances like this will continue, although we hope Americans from across the political spectrum can ease up on the character assassinations and stop weaponizing mob mentality.
"It is our hope that what has transpired can serve as an example for all of us to realise the enormous responsibility we have to ourselves and to each other regarding the use of our written words when we etch them in digital stone; that we as a society may learn from this experience and in the future we will think twice before we decide what we want to express; and in doing do learning perhaps can harness this capability to help and heal instead of hurting each other.
"Thank you for taking the time to read our words."
Alongside the statement, Pratt wrote: "Although I don't support James Gunn's inappropriate jokes from years ago, he is a good man.
"I'd personally love to see him reinstated as director of Volume 3. If you please, read the following statement- signed by our entire cast."
Gunn had been writer and director of the Guardians Of The Galaxy franchise from the start, taking the relatively obscure Marvel Comics title about a group of misfits and turning it into two huge hits that together totalled more than $1.5 billion in global box office revenues.
After his tweets emerged, the filmmaker issued a statement apologising.
He said. "My words of nearly a decade ago were, at the time, totally failed and unfortunate efforts to be provocative.
"I have regretted them for many years since - not just because they were stupid, not at all funny, wildly insensitive, and certainly not provocative like I had hoped, but also because they don't reflect the person I am today or have been for some time.
"Regardless of how much time has passed, I understand and accept the business decisions taken today. Even these many years later, I take full responsibility for the way I conducted myself then."
He also posted several tweets saying he was sorry for trying in the past to get laughs through shock value.