Plaid to name new leader from Lord Elis-Thomas, Elin Jones, and Leanne Wood
Plaid Cymru will unveil its new leader later, at the climax of an election of party members.
Three candidates, all Welsh assembly members, are in the running for the party's top job: Lord Elis-Thomas, Elin Jones and Leanne Wood.
Outgoing leader Ieuan Wyn Jones is standing down after a decade at the helm.
His successor will be announced after ballot papers are counted in Cardiff.
The election has taken place under the alternative vote system, where members rank candidates in order of preference.
If no-one get 50% of the first-preference votes, the third-placed candidate is eliminated and their second-preference votes come into play.
Helen Mary Jones, chair of Plaid Cymru, told BBC Wales that the day was a "watershed" for the party in determining its future direction, whichever candidate won the leadership election.
She said: "They're all keen to be in government but the question is under what circumstances, what would be the priorities, what would we deliver for the people of Wales in government?
"The priority for the new leader has got to be building the party, making the case for independence and putting us in a position where we can make major gains in the next assembly election and, of course, the Westminster election that comes before it."
Ms Jones also praised the contenders for showing "common ground" and "fresh thinking" throughout the campaign, helping unite and boost the party's fortunes after its electoral setbacks.
"I know that whoever wins today will be building on the strengths and talents of the other two candidates as a key part of their team to lead and move Wales forward," she said.
"We have to show people that while the other parties may talk about being Welsh and they may wrap themselves in the dragon flag when it suits them, there is only one political party that makes policy for Wales, policy made by the people of Wales, and that is Plaid Cymru.
"The candidates have been saying themselves that we've very often won the argument but lost the election.
"We now have to start winning the argument and winning the elections, and that's where our new leader will be leading us forward."
Party chief executive Rhuanedd Richards said it was a "momentous day for Plaid and for Wales".
"The leadership election has energised and united Plaid with a renewed determination to fight for a better future for Wales," she said.
The result is expected on Thursday afternoon.
The party paid tribute to Mr Jones, who said he would stand down after disappointing election results for the party last May.
Plaid AM Alun Ffred Jones said he had led Plaid into government through its coalition with Labour in 2007 and helped secure a Yes-vote in last year's referendum on giving the assembly direct law-making powers.
"Wales would not be the nation it is today had it not been for Ieuan's leadership," he said.