Arday, who was diagnosed with autism and other developmental difficulties as a child, had disputed the allegations against him.
But he said in a public resignation letter on August 5 that he had “reached the limits of what any person should reasonably be expected to endure”.
The cause of his death has not been made public, with police saying only it was not suspicious and they were preparing a file for a coroner.
MP Diane Abbott, the first black woman ever elected to the UK parliament, told the rally organised by campaign group Stand Up To Racism that she saw Arday a week ago.
She said: “He felt he had no choice but to resign. And he must have felt that if he resigned, the attacks on him would stop. But, in fact, they got even worse from his resignation to his suicide last week.
“It wasn’t just a campaign against the professor. It was a campaign against all of us.”
Stand Up To Racism said some 30,000 people attended today’s rally, although AFP could not immediately confirm the figure.
Many were dressed in black, carrying roses and sunflowers as well as banners saying, “Rest in power Professor Jason Arday”.
Claire Lynch, 69, a retired dyslexia teacher, told AFP she had been “horrified” by what had happened to Arday, saying he had been “hounded”.
She said: “I spent a lot of my life teaching my pupils that they could do anything, if they put their mind to it. And to see someone brought down who was doing exactly that – he would have been someone I was holding up as an example.”
Alex Pascall, 89, said Arday’s death should serve as a “wake-up” call, saying it was “time for these type of things to stop”.
A separate, smaller vigil was also held in Cambridge.
An online fundraising page created by racial equality campaigner Patrick Vernon to support Arday’s family had raised more than £174,000 ($398,000).
Separately, a petition demanding an immediate public inquiry into the media coverage of Arday had gathered more than 90,000 signatures – including from Abbott and Green Party leader Zack Polanski.
Addressed to Prime Minister Andy Burnham, the petition posted by activist group Good Law Project claimed Arday’s death was “the direct, foreseeable and foreseen result of press harassment”.
A similar vigil to the one in London was held in Market Square in Cambridge. Photo / Chris Radburn, AFP
Downing Street declined to say whether any inquiry was planned, repeating Burnham’s comments at the weekend that it was a time for “reflection”.
The petition said Arday’s death came after “two weeks of relentless harassment”, stressing that “racism lay at the heart of this story”.
The university is also facing questions over its handling of the allegations and its treatment of Arday.
Former students of Arday have created a website called Everything Good About Jason Arday, asking people to share memories “about the kindest person we knew”.
Last week, before the announcement of Arday’s death, Cambridge’s vice-chancellor Deborah Prentice announced an investigation into the circumstances of his appointment and his time working at the university.
– AFP