On 20 June 2013, the former Plaid Cymru leader
Ieuan Wyn Jones resigned from the
Welsh Assembly seat of Ynys Môn in order to take a post leading the new Menai Science Park, triggering a
by-election in the constituency. In June 2013, BBC Cymru Wales announced that ap Iorwerth had stepped down from his role as a news presenter to pursue a Plaid Cymru nomination for the by-election. The by-election provoked a local debate, in which
Wylfa Nuclear Power Station became a key issue. The by-election was seen as key, and had
Welsh Labour won then they would have had an outright majority in the Assembly with 31 out of the 60 seats. The election on 1 August 2013 saw ap Iorwerth gain 12,601 votes, over the second-placed candidate Labour's Tal Michael (3,435 votes), on a turnout of 42.45%. In January 2014, he was appointed as Plaid Cymru's spokesperson on Economy and Enterprise, which also included Transport. Ap Iorwerth held his seat in 2016. Shortly after those elections, he was appointed as Shadow Minister for Health, as Plaid Cymru had become the second largest party. In October 2016 this ceased to be a shadow cabinet role, as Plaid ceased to be the second largest party. He unsuccessfully ran for the
leadership of Plaid Cymru in 2018, losing to
Adam Price. He was later appointed as joint deputy leader, and as Plaid Spokesperson for Economy and Finance. He also took responsibility for the Plaid Health portfolio in February 2020. In May 2021, he was reshuffled to just the Health and Social Care portfolio. In July 2022, he announced his candidacy to become Plaid Cymru's
prospective parliamentary candidate in
Ynys Môn for the
2024 United Kingdom general election. In October 2023 he was replaced as candidate by
Llinos Medi. In March 2023, as Plaid Cymru's spokesperson on health and care, ap Iorwerth called for a public inquiry into Betsi Cadwaladr health board failures and repeatedly called to replace Betsi with smaller health boards. In 2025, Rhun ap Iorwerth was inducted to the
Gorsedd at a ceremony during the
National Eisteddfod of Wales at Wrexham.
Leadership of Plaid Cymru In May 2023, ap Iorwerth announced he was running to become leader of Plaid Cymru. He was
elected unopposed. On 17 March 2024, ap Iorwerth announced an early conclusion to the
co-operation agreement between
Welsh Labour and Plaid Cymru, stating "I remain deeply concerned that the First Minister
Vaughan Gething has failed to pay back the £200,000 donation to his leadership campaign from a company convicted of environmental offences, and believe it demonstrates a significant lack of judgment". In the
2026 Senedd election, he won a seat in the
Bangor Conwy Môn constituency. In January 2026, he said he preferred to form a
minority government than a
coalition government. Political Scientist
John Curtice predicts
Plaid Cymru will win be the largest party in Senedd with between 41 and 46 seats, and
BBC News speculating he will become
First Minister of Wales. ==Notes==