Edwin Poots has resigned as leader of the Democratic Unionist party (DUP) after colleagues rebelled over a deal to revive the Northern Ireland assembly, triggering a new political crisis in the region. Poots quit on Thursday night after just 21 days in the job, the latest drama in a leadership meltdown in Northern Ireland’s biggest party that could sink the power-sharing assembly at Stormont. The 55-year-old left an emergency meeting at the party’s Belfast headquarters without addressing waiting media and later released a statement saying he had asked the party chairman to start an electoral process for a new leader. “The party has asked me to remain in post until my successor is elected,” said the statement. “This has been a difficult period for the party and the country and I have conveyed to the chairman my determination to do everything I can to ensure both unionism and Northern Ireland is able to move forward to a stronger place.” The humiliating fall throws into doubt a deal on Irish language legislation announced on Thursday. The deal was designed to defuse a stalemate with Sinn Féin and allowed Poots’s protégé, Paul Givan, 39, to become Northern Ireland’s youngest ever leader on Thursday. Instead the deal backfired on Poots, damaged Givan and added a new chapter to DUP turmoil that has been likened to a soap opera. The issues originate with Brexit. The DUP backed the UK’s departure from the EU, torpedoed Theresa May’s proposed Brexit deal and paved the way for the rise of Boris Johnson, only to be betrayed by his promise to not impose trade checks in the Irish Sea. With many unionists blaming the DUP for the own-goal – and loyalist protesters taking to the streets – Poots and others in the party staged a putsch against Arlene Foster in April. The Stormont agriculture minister – a creationist from the Paisleyite wing who believes the Earth is just 6,000 years old – narrowly defeated Sir Jeffrey Donaldson in a leadership contest that split the party into warring factions. Poots then stumbled at the first hurdle – reviving the Stormont executive. When Foster stepped down as first minister on Monday so too, under Stormont rules, did the deputy first minister, Sinn Féin’s Michelle O’Neill. Sinn Féin’s price to reboot the executive under a Givan-O’Neill partnership was commitment on a long-promised Irish language act. That is anathema to many in the DUP. To avoid the collapse of Stormont – and a snap election that could annihilate the DUP – Poots agreed to a British government-brokered deal that would let Westminster pass such legislation. Ignoring protests from DUP assembly colleagues and MPs on Thursday morning, Poots nominated Givan as first minister, only to find himself ousted hours later, leaving a question mark over the future of Givan and the entire executive. The favourite to take over the DUP will be Donaldson. During last month’s leadership contest the MP said it was a mistake by Poots to split the party leadership and first minister post. However, for Donaldson to become first minister he would have to resign as MP, be elected to Stormont – and then face the same Sinn Féin demand over Irish language legislation. “It doesn’t matter who the leader of the DUP is because they will face the same critical issues which were negotiated and agreed on their watch,” said Doug Beattie, leader of the rival Ulster Unionist party. “Unionism deserves better and Northern Ireland deserves better.” In a tweet, Tim Farron, who led the Liberal Democrats for two years, marvelled at the brevity of Poots’s tenure. “Seriously, even I lasted longer than that,” he wrote. Other commentators compared Poots to a football manager.