Steve Benson, a town councillor in Mirfield, has left the Conservatives to join the Greens.
The Greens made 60 gains nationally during the local elections in May and last week saw former Lord Mayor of Sheffield, Green councillor Magid Magid, elected to the European Parliament.
In Kirklees the Greens consolidated their base in Newsome ward by doubling their majority with new candidate Sue Lee-Richards.
Clr Benson, who represents the Crossley ward on Mirfield Town Council, said he had joined the Greens as he felt he could do more for the environment and flooding problems around the River Calder.
He was also at the forefront of a determined campaign to stop pastureland at on Balderstone Fields in Mirfield being turned into a housing estate.
He commented: “As a Green Party councillor I will continue to carry out the hard work I have done for Mirfield over the last four years.”
In the local elections the Greens became the new challengers to the Conservatives in Mirfield ward, pushing Labour into third place by just one vote.
Clr Andrew Cooper, the Green group leader on Kirklees Council, said it was “great” to welcome Clr Benson to the party.
“I’ve seen many of the environmental projects Steve has championed on the Project Mirfield website and it is clear he will be a real asset to the Green cause as he already is to the community he represents.”
He added: “As Steve has joined the Green Party this means that we now have representatives on four out of the five parish councils in Kirklees.
“In the local elections we won ten seats on Kirkburton Parish Council.
“In Wooldale ward Darryl Gould topped the poll to become our representative on Holme Valley Parish Council and Sonia King has recently been co-opted onto Meltham Town Council.
“What they all share is a positive commitment to improve the environment in the area they live and I look forward to working with them.”