Rhun ap Iorwerth has been voted first minister of Wales after Plaid Cymru’s Senedd electoral victory ended 100 years of Labour hegemony and held off Reform UK.

Ap Iorwerth was confirmed after a plenary vote on Tuesday with the support of the 43 members of his party in the Senedd and the two Greens, while Welsh Labour and the sole Liberal Democrat in the Siambr, the debating chamber, abstained.

Reform UK’s Dan Thomas, the new leader of the opposition, and the Conservative leader, Darren Millar, also put their names forward for first minister.

Ap Iorwerth, who is pro-Welsh independence, received a standing ovation from his MSs and the public gallery as the ballot result was announced. He said: “It is the greatest privilege of my life to be elected first minister in a nation that means so much to me.

“Something has stirred in the soul of Wales – a new confidence, a new hope, a new broader horizon, never to be narrowed again by the naysayers with other priorities in other places.

“My promise to everyone is that I will lead without prejudice or presumption. I’ll never take this privilege for granted.”

Ap Iorwerth paid tribute to his predecessor, Labour’s Eluned Morgan, saying she had governed “with resilience and determination” and “steered her government with enthusiasm and with pride at all times”.

Plaid Cymru ended Labour’s century-long electoral dominance in Wales in last week’s elections, winning the most seats in the newly expanded 96-seat parliament. Reform, which had hoped to be the biggest party, won 34 seats, and Labour came third with just nine seats, marking a definitive end to the party’s grip on its birthplace.

The Conservatives returned seven seats, the Liberal Democrats one, and the Green party gained two MSs for the first time.

Morgan lost her seat, triggering a leadership contest in Welsh Labour. Ken Skates, the Senedd member for Fflint Wrecsam and the former cabinet secretary for transport, has taken over as interim leader.

Thomas, of Reform Wales, told the Senedd that his party would be a “robust opposition” to Plaid Cymru government. “I would like to remind Plaid Cymru that this chamber has a pro-union majority … The future of a prosperous Wales lies within a successful United Kingdom and Reform will ensure that that union prevails,” he said.

“The people of Wales made that clear at the ballot box and Reform serves the people of Wales.”

Under Wales’s new and more representative electoral system, at least 49 seats are needed for a majority. No party was likely to win that, but Friday’s results put Plaid Cymru in a comfortable position to form a minority government.

Ap Iorwerth previously told the Guardian he would seek out mature cooperation from all opposition parties on a case-by-case basis, and that his administration would press the UK government for extra powers over policy areas such as policing and justice, rather than engaging in political rows with Westminster.

Plaid Cymru has ruled out an independence referendum in the next Senedd term, but the party has repeatedly said it will use its time in government to make the case for an independent Wales.

The Senedd also voted for Labour’s deputy leader, Huw Irranca-Davies, to be the new llywydd, or speaker, before the first minister vote could take place. Kerry Ferguson, of Plaid Cymru, was elected deputy presiding officer.

The speaker role must be held by a member of the opposition. The vote was triggered when Elin Jones, who served as a Plaid Cymru llywydd for a decade, stood down from the position at the end of the last parliamentary term.

Ap Iorwerth, 53, grew up on Ynys Môn (Anglesey). He worked as a BBC journalist in Cardiff and Westminster before entering politics in 2013, and became Plaid Cymru leader in 2023.

He will be sworn in by a high court judge on Tuesday afternoon, and is expected to begin appointing cabinet secretaries on Wednesday.