Misan Harriman will not seek another term as chair of the Southbank Centre and is to step down in autumn after a month of intense pressure caused by accusations he shared a conspiracy about the Golders Green attack.

Harriman, who has held the position since 2021, confirmed in a social media post that he would not continue as chair beyond autumn.

He said: “It’s semi-public knowledge that my term is coming to an end anyway … I had decided way before this madness that I was going to do two terms.

“It takes a long time to find whoever the next chair will be, and that process will begin at some point, and I’ll update you more on exact dates and timelines probably in autumn.”

Harriman praised the centre’s board and highlighted Harry Styles’ Meltdown festival, Anish Kapoor’s new show at the Hayward and the upcoming Nan Goldin show as evidence of an institution in fine health.

He called the Southbank Centre, which is celebrating its 75th year in 2026, “a sacred 11 acres” and said he was “still very proud to be chair”.

His departure comes after a month of intense scrutiny and criticism of his social media activity, although the Southbank confirmed Harriman had made the decision to depart in January.

Harriman has more than 500,000 followers on Instagram after rising to prominence as a photographer of Black Lives Matter protests. In May, he was accused by the Telegraph of sharing a social media post that contained a conspiracy about the Golders Green attack because it questioned the amount of coverage given to the Muslim victim, Ishmail Hussein.

Critics of Harriman said the repost risked minimising the antisemitic nature of the attack, with newspaper editorials calling for him to resign as chair of the Southbank.

He was also criticised after England’s local election results, for making comments about Reform voters. One headline read: “Southbank Centre chief ‘compares Reform victory to Holocaust’”, after Harriman quoted Susan Sontag in a video giving his thoughts after Reform’s gains.

He said: “She said when thinking about the Holocaust, 10% of people in any population are cruel no matter what, and 10% is merciful no matter what and the other – this is important – the other remaining 80% could be moved in either direction.

“It’s such a profound way to look at us. In the context of yesterday’s election result, it is something which I think is really topical.”

A Times editorial called his online comments “crass” and “distasteful in the extreme”.

“Mr Harriman is the head of a high-profile body in receipt of public funds. That position inevitably amplifies his private views,” it wrote. “His remarks risk damaging the reputation of the Southbank Centre and driving away sponsors.”

Greta Thunberg, Tracey Emin and Gary Lineker were among those to sign an open letter in support of Harriman, after what they said was a “dishonest smear campaign” by media outlets.

The culture secretary, Lisa Nandy, received letters from parliamentarians condemning Harriman and also supporting him, with a letter signed by peers and MPs saying there was a “smear campaign” against Harriman “seemingly aimed at whipping up a furore to engineer an ever-growing environment of cancel culture”.

The Southbank chair lodged an official complaint with Independent Press Standards Organisation (Ipso), the press watchdog, about the coverage, which included pieces by the Times, the Telegraph and GB News.

An online campaign of support for Harriman garnered more than 100,000 signatures.

Harriman did not address the accusations made against him in the video other than referring to “this madness”, and a spokesperson for the Southbank Centre told the Guardian his departure had nothing to do with the recent “antisemitism” row.

The spokesperson said: “Misan confirmed with the deputy chair in January that he would not be seeking a third term and would step down in the autumn of 2026.

“Succession planning is already underway, with further details to be confirmed following our AGM in July.”