As well as the more proportional system in 2026, the number of seats in Cardiff Bay will increase from 60 to 96 and polling suggests Plaid is in a strong position, external to challenge Labour.
It remains likely a deal of some kind will have to be struck between two or more parties to form a government following the next election.
But ap Iorwerth told journalists before the conference he “can’t see a scenario” where Plaid would co-operate with the Welsh Conservatives or Reform UK.
During his speech at the Principality Stadium, ap Iorwerth will announce he would appoint a minister for public health if he were to become first minister in May 2026.
The move would be part of Plaid’s approach to supporting the NHS by investing in preventative health measures.
Ap Iorwerth will tell party members a Plaid Cymru government would “break the cycle of short-term thinking which short-changes Wales”.
“For too long, Labour’s priority has been managing people’s pain, but I want to keep people healthy and I can announce that in the first 100 days of a Plaid Cymru government we will bring forward a new budget – based on the principles of a healthier, wealthier Wales – with a promise that spending on preventative health measures will increase every year.
“No more sticking plaster, no more blaming the individual, no more passing the buck.”
He will say a minister for public health will ensure “a truly national mission of creating healthier lives which in turn delivers substantial savings”.
Ap Iorwerth will also commit to “clearing the emergency maintenance backlogs” at Welsh hospitals before 2030.
Earlier this week a critical incident was declared at Bridgend’s Princess of Wales Hospital after long-term damage was found to its roof.
