Sadiq Khan, who has severe asthma, was vaccinated at Mitcham Lane Baptist Church in Wandsworth on Friday.
He said it was "fantastic" that more than 1.5 million Londoners had received at least one dose of a Covid vaccine.
The rollout of the vaccines was "a testament to the hard work" of scientists and NHS staff, he added.
The mayor said: "I urge everyone who is offered it to take it as soon as possible".
"The widespread rollout of these vaccines will protect us from serious illness, will help us all to get back to the things we have missed and let us see the people we love," he added.
Dr Penny Osborne, who works at the clinic at Mitcham Lane Baptist Church, said the rollout was "progressing well" and the speed was thanks to a "fantastic level of community support".
"We are now focusing our efforts on inviting those aged 16 - 64 who are in at-risk clinical groups, which includes Sadiq," she said.
It’s easier to ask forgiveness than it is to get permission.