imon Lee said he was hugely impressed by the leadership of Colum Eastwood and Claire Hanna, and the party was a “perfect fit for him”.
Mr Lee admitted that the Greens’ disastrous Assembly election result, in which it lost both its MLAs, “may have been a factor” in his departure.
A Presbyterian, he comes from a unionist background. He has a degree in divinity, considered becoming a minister, and describes himself as “a person of faith”, but he supports the SDLP’s position on Irish unity.
A Carryduff native, he was elected onto Lisburn and Castlereagh City Council in 2019 and is running again in next year’s local government election.
Mr Lee (43) joined the Greens eight years ago. “I always had climate change concerns, but having children motivated me to take action to save the planet for future generations,” he said.
Asked why he had left the party, he said: “It wasn’t an easy decision but I already feel welcomed, wanted and valued in the SDLP.
"I am a social democrat, and the party’s policies on social and economic justice, well-funded public services, protecting the environment and challenging the decisions which have led to climate change reflect my own beliefs.
"I decided Alliance wasn’t for me because they are too right-of-centre.”
Asked if internal tensions in his former party had led to his resignation, Mr Lee said: “I’m not interested in having a go at the Greens. I don’t want to get into that.
"I want to leave on good terms. I want to depart in a positive manner out of respect for those friends I’ve known for so long.
"I bear no ill-will to anyone in the Greens. I’ve built lasting friendships with good people doing great work in their own communities. I wish them well, but this is the right move for me.”
Asked if the defeat of Clare Bailey in South Belfast and Rachel Woods in North Down had influenced his resignation, Mr Lee said: “There is no doubt that losing the two Assembly seats was a bitter blow.
"It may have been a factor in my departure, but it’s much more complicated than that. The SDLP had a very tough election too. There is no security in politics.”
On the Greens’ future, Mr Lee said: “It will be a big ask to win back those Assembly seats in the short-term. They have a mountain to climb. The bad election result wasn’t down to any failing of the Greens, it was just the rise of Alliance.”
A lecturer in religion at Belfast Metropolitan College, Mr Lee described his journey from a unionist background to a party which supports Irish unity.
"My family emigrated to Canada in 1987 and I went to school in Toronto," he explained.
"I came home and said to my dad, ‘There are Catholics in our class’ and he said ‘That’s the way it is over here. They don’t care about those things.’ I wondered why we were segregated in Northern Ireland.
"When we returned home, I was a unionist by default because that’s how I was brought up. My first vote was in the 1998 Assembly election after the Good Friday Agreement, and it was for a unionist party.
"The year before I started at Queen’s University, I was in Chicago on a student exchange programme. The Americans loved the Irish. They didn’t grasp partition. They saw no difference between us and the Republic. If you came from Northern Ireland, you were Irish.
"I began to feel more Irish. I started Queen’s as a moderate unionist but, by graduation time, I’d stopped being one.”
Mr Lee said that, post-Good Friday Agreement, people felt “freer to explore their identity”.
He said: “I travelled more to Dublin, Galway and Cork. I felt a connection with those places. I didn’t see them as a foreign land, I felt I belonged there.
“I like the SDLP’s idea of a new Ireland, there’s something exciting about it.
"It’s not about holding onto the past, it’s about exploring fresh possibilities. Some people might think that’s strange for a Protestant, but I don’t believe it’s that unusual post-Brexit.
"Brexit exposed the democratic deficit here. Even if 100% of people had voted remain, it wouldn’t have made any difference — that doesn’t feel right. The SDLP’s new Ireland policy is sensible, positive, and measured.”