Plaid Cymru took both seats from Labour in Caerphilly County and Van Community Council by-elections.
The latest Plaid successes in Caerphilly follow the Senedd by-election and Penyrheol council byelection wins late last year.
The votes for the county were Plaid Cymru 374, Reform 246, Labour 231 and Liberal Democrat 12 and for the Van Community Council ward it was Plaid Cymru 234 and Reform 141.
Congratulations to Jeff Grenfell and Alison Vyas.
Councillor Charlotte Bishop, leader of the Plaid Cymru group on Caerphilly County Borough Council, said: “I couldn’t be prouder today. Congratulations to Jeff on winning the county by-election and to Alison on being elected to the community council seat in Van ward.
“I’m very pleased that the voters of Van ward have firmly rejected the divisive politics of Reform UK.
“I’ve watched them both put the time in – the quiet conversations, the listening, the turning up when no cameras are there. They don’t do this for recognition, and they don’t make grand promises. They do it because they genuinely care about people.
“What matters most to me is heart — and both of them have it in abundance. They look after their communities the way family should: patiently, kindly, and with respect for every voice.”
Senedd Member Lindsay Whittle said: "I'm delighted at the result but shocked that only three people from Reform even bothered to turn up at the county. They said nothing and left at the end and their council council candidate who was from Cefn Hengoed made no effort during the campaign."