The former bus conductor, who rose to become vice chairman of Transport for London (TfL) during Ken Livingstone's spell as London mayor, said he made the move due to "policies not personalities".
He told getwestlondon he was particularly drawn by the party's commitment to pursue nuclear disarmament and the creation of a 'land value tax'.
He said the latter would see people taxed based on the value of the land they owned, rather than any buildings on it - a policy he said would discourage the hoarding of disused land, lowering house prices and driving business growth.
He also said he found the Greens more democratic, with all members given the chance to get issues of their choice debated at the party's annual conference.
"The Labour Party has been good to me but after 50 years of membership, joining the Green Party has been like a breath of fresh air," he said. "The member involvement and open democracy in the Green Party is intoxicating - as are its policies of creating a fair economy that works for all by making the minimum wage a Living Wage and introducing a basic income, and creating a sustainable and stable society by tackling climate change and investing in renewables.
"The Green Party's policies are at the cutting edge of what we need in this society and they are about building real political change - change that works for the public. That's why my heart is now firmly with the Greens."
Mr Wetzel has been organising '100% Green', an initiative to field a Green Party candidate in every constituency at the upcoming general election.
The party fielded a representative in just half the constituencies in 2010 and originally set a target of 75% for these elections, but he has helped boost that to between 85 and 90%, with the full list of nominations yet to be totted up.
He insisted nothing less than victory would be a good result for the Greens in Hounslow's two constituencies, where the party finished fifth and sixth in 2010.
Mr Wetzel, who lives in Brentford, was first elected as a councillor in Hounslow in 1964, aged 21, and served for four years. He was re-elected in 1986 and was leader from 1987 until 1991, when he stood down.
He began his career as a bus conductor at Hounslow bus garage and later served as a flying staff roster officer at British Airways for five years.
He was chairman of the transport committee on the Greater London Council - the predecessor of the Greater London Authority - during the 1980s.
As vice chairman of TfL from 2000 to 2008, he oversaw the introduction of the congestion charge, among other big changes.
His spell in the hotseat at Hounslow Council coincided with the creation of Hounslow Urban Farm and New Chiswick Pool.
He said he strongly opposed the current Labour council's plans to lease part of Brent Lea Recreation Ground, in Brentford, to a new free school.
"It's absolutely criminal to be building on a park in Brentford where more public space is needed," he told getwestlondon. "If you had a land value tax, land would be cheaper and the council would be able to purchase private land for a school."