The campaign to reinstate Ian Parker, co-director of the university's Discourse Unit, which promotes "radical theory and practice" in psychology, has been launched by students and staff outraged at his removal from campus.
His supporters claim they have been given "little to no explanation" about the disciplinary charges against him.
They also say that he has been "silenced" after raising concerns about his department - a claim denied by the university.
Professor Parker is the co-founder of Psychology Politics Resistance, an international network of psychologists opposed to abusive uses of the discipline.
The online petition to reinstate Professor Parker describes him as "one of the most respected and influential scholars in the contemporary critical psychology", whose work is followed by hundreds of psychologists across the world.
China Mills, a PhD student at Manchester Met, said the "sudden" suspension had greatly affected his students.
"For his students Ian has simply 'disappeared' overnight, and while he is keen to continue supervising and teaching, he is not allowed to," she said.
A university spokesman confirmed "a professor has been suspended in accordance with the terms of its disciplinary procedure, pending an investigation into allegations of gross misconduct".
"Whilst it can obviously not comment on the exact nature or content of the allegations while they are being investigated, it can confirm that external speculation around the reasons for the suspension is wholly inaccurate," he said.