Irfan Rabbani will join the SNP opposition group on the council, which Labour controls with a majority of 15.
The 49-year-old said he would not be standing in the local elections in May although he would be campaigning for other SNP candidates.
Mr Rabbani has represented Glasgow's Pollokshields ward since 2007. He had been a Labour member for 20 years.

A 24-hour tube strike is due to go ahead after unions rejected a "new deal" from Transport for London (TfL).
But Sadiq Khan has instructed TfL "to continue negotiating".
Workers from the RMT and the Transport Salaried Staffs' Association (TSSA) unions are scheduled to walk out from 18:00 GMT.
The strike is expected to cause mass station closures.
Tube strike guide: What you need to know
The Labour mayor said TfL's negotiating team would "be available around the clock to resolve this dispute".
Calling the strike "pointless" Mr Khan said TfL's offer would "ensure station safety and staffing levels across the Tube network".
Steve Griffiths, chief operating officer for London Underground (LU), said the process had already begun to hire 200 extra station staff.
"Taking into account existing vacancies and natural turnover this means that over 600 staff will be recruited for stations this year."
The biggest rail union, the RMT, had walked out of talks at conciliation service Acas on Saturday.
On Sunday, the TSSA announced it had rejected the deal after consulting its members overnight.
TSSA general secretary Manuel Cortes said the new deal would not "restore Tube safety levels" with the "urgency that is now needed".
The offer was made after RMT left the meeting, a point the RMT disputes.
In a message to its members, RMT regional organiser John Leach said the talks had "failed" and the strike would go ahead.
Talks between both unions and London Underground (LU) had previously broken down on Friday afternoon.
No details of the latest deal were revealed but Mr Leach told members of the RMT that LU had "given exactly the same offer again" during Saturday's last-ditch talks.
"This is just not acceptable. The unsafe practices and pressure on staff and passengers have to be resisted and will be," he said.
Transport for London (TfL) previously said it would address the recommendations of a recent report, which found the closure of ticket offices had caused "significant issues" for Tube passengers.
A Labour councillor in Glasgow who had been de-selected by the party has defected to the SNP.
[NEXT_CONCEPT]
The Mayor of London has called for "last-ditch" talks to avert a strike on the London Underground hours before it is due to begin.