Congress had refused ticket to Desai from suburban Goregaon in the last month's Maharashtra Assembly elections.
Speaking to PTI, Desai, who was elected as a corporator on the Congress ticket twice, said the party gave ticket to "a candidate who was well-connected to Delhi rather than Goregaon" in the Assembly polls.
He joined BJP here today in the presence of state Minister Vidya Thakur and Mumbai BJP chief Ashish Shelar.
"For the past many years, the seat was given to NCP which we were saying was a mistake. It was proved this time as the NCP lost terribly there. We then took a decision not to take things lying down and then the option we had was BJP," he said.
Kamat remained unavailable for comment.