Northern Ireland has a new first minister, Paul Givan of the Democratic Unionist party (DUP), after a deal on Irish language legislation averted a crisis that had threatened to cause the region’s government to collapse. Givan, 39, became Northern Ireland’s youngest ever leader on Thursday after taking his post alongside Michelle O’Neill of Sinn Féin, who resumed her position as deputy first minister. The nominations restored the Stormont assembly and executive after a week of turmoil that had raised the prospect of a snap election. However Edwin Poots, the DUP leader who nominated Givan, faced an internal party backlash against the Irish language deal that could destabilise his leadership and weaken Givan’s authority in the executive. Party dissenters said Poots ceded too much to Sinn Féin in a deal brokered on Wednesday night by the British government. The Northern Ireland secretary, Brandon Lewis, announced the breakthrough early on Thursday. The deal commits the British government to introducing an Irish language act in Northern Ireland if the Stormont assembly fails to do so by the end of September. “Following my intensive negotiations with the parties over the last few days, today I can confirm that if the executive has not progressed legislation by the end of September, the UK government will take the legislation through parliament. If that becomes necessary, we will introduce legislation in October,” Lewis said. The legislation would include the creation of an Ulster Scots commissioner, an Irish language commissioner and an office of identity and cultural expression, said Lewis. Sinn Féin says the legislation – promised in previous power-sharing agreements with the DUP and other parties – will show respect and equality for Irish language and culture. Many unionist politicians say nationalists have “weaponised” the language to undermine the region’s sense of Britishness. Sinn Féin’s leader, Mary Lou McDonald, welcomed the deal. “Tonight we have broken through all of that. Irish speakers have been waiting for 15 years for basic rights and recognition to be delivered.” Sinn Féin had demanded such a commitment as the price of rebooting Stormont after Arlene Foster stepped down as first minister on Monday. She had already resigned as DUP leader following a party revolt in April fuelled by anger at the Northern Ireland protocol. With the DUP riven by in-fighting and blame over the Irish Sea border, Poots wished to resolve the stalemate at Stormont and avert an early election. However, most of the party’s assembly members and peers reportedly opposed the language deal in a closed-door meeting described as “bedlam”. Poots ignored the revolt and nominated Givan, allowing the executive and assembly to resume business, but Poots’s authority is badly damaged. Some analysts are already writing his political obituary and predicting an early election. “It is a day of indisputable victory for Sinn Féin, it is a day of shame and humiliation for the DUP,” said Jim Allister, leader of Traditional Unionist Voice, a DUP rival. Accepting the first minister post, Givan thanked Poots, his political mentor, and paid tribute to his predecessors, Ian Paisley, Peter Robinson and Foster. “They all had their own way of leading and I will have mine. Mistakes I am sure I will make, I am not infallible. There is much goodwill from the public for this place to work. We must all recognise that there is much more that we have in common than separates us.” O’Neill said the executive’s priority would be vaccinating people against Covid-19 and reviving the economy.