Gareth Arnold announced on Twitter he would be standing as an independent in the constituency, where the public has gone largely unrepresented since Mr O’Mara stopped attending Parliament in April, apart from three days last month where he did return to Westminster for Brexit votes.
Mr Arnold dramatically resigned by taking over Mr O’Mara’s Twitter account in July as he said he could no longer sit back and watch Mr O’Mara have such “contempt for his constituents” and believed “something big needed to happen”.
Despite the acrimony, Mr O’Mara later described Mr Arnold as the “Noel to his Liam”.
But now Mr Arnold has insisted Mr O’Mara is “not [his] mate” and he tweeted : “If elected as MP for Sheffield Hallam I would want the office to be held accountable with oversight from a community group made up of constituents. This includes a monthly forum to discuss ideas and issues.”
He also said he would hold weekly six-hour surgeries, and improve social and mental health care provision, support for the homeless, and green policies.
But when asked whether he would be standing against his former boss - who has not yet announced whether he will throw his hat into the ring - Mr Arnold said: “Your guess is as good as mine.”
Replying to concerns over his involvement with Mr O’Mara on Twitter, Mr Arnold admitted the period was “atrocious” and said: “I want to make sure that never happens again.”
He said: “If you remember I called him out on his b*******. No other staffer did. Hallam needs someone [to] represent them not an O’Mara follow up act. I care about Hallam.”
He added: “I recognise in some people's minds I'm not the ideal candidate but I hope my compassionate and drive will connect with voters.”
He said he had “secured considerable funding” and “would actually turn up”.
Mr Arnold also assured followers he and his team would be fully security vetted, after he revealed to the BBC that he was not security cleared during his time with Mr O’Mara’s office.
At the time he told the BBC: "People have joked to me that I was basically the MP for Sheffield Hallam because Jared was so, erm - not here basically…”
In July, Mr O'Mara announced he would step down after a series of problems which saw him suspended from the Parliamentary Labour Party and then resign from the party.
But the Treasury, which administers MP resignations, later announced that he had postponed this decision.
It is not yet clear whether he will stand in the December General Election.