The actor, who played headteacher Pete Hamill, explained that he made the decision to bow out to pursue other roles.
Mitchell wrote on Twitter this morning: "To those asking, I can officially confirm that I have left Oaks to concentrate on other projects.
"I'd like to thank u all for ur love and support throughout the year, it's greatly appreciated... (sic)"
Mitchell starred in one-off comedy Rick and Peter last month and has recently landed a role in BBC Three sitcom White Van Man.
Mitchell added: "I start filming on #WhiteVanMan next week and fingers crossed we get a series of #RickandPeter."
It is thought that viewers have already seen the final scenes featuring Pete, who was first introduced to Hollyoaks at the beginning of the year as an old friend of show favourite Brendan Brady (Emmett Scanlan).
Pete's storylines also saw bitchy schoolgirl Ruby Button (Anna Shaffer) develop a crush on him after he started giving her extra tuition.
> Read our recent interview with Peter Mitchell
> Read more Hollyoaks spoilers and news
Watch Hollyoaks' teaser video for this week's episodes below: