The former Prime Minister addressed a room of around 200 activists as part of Pat McFadden's campaign to get elected for a fifth time in Wolverhampton South East.
Speaking at Blakenhall Community and Healthy Living Centre on Bromley Street, Mr Blair said people should not believe Boris Johnson's pledge to make Britain a fairer society.
WATCH: Tony Blair on why he's backing Pat McFadden
"I say to anyone in this election who thinks it might be wise to switch from Labour to Tory, remember what the Tories do to communities like this.
"Never put them in charge of the country if you can help it."
Mr Blair said he still is still supporting the Labour Party despite his well documented differences with Jeremy Corbyn.
During his visit he posed for pictures with members of the crowd and chatted with supporters.
Former minister Mr McFadden, who had introduced Mr Blair as "a proven winner", said: "People know what my kind of Labour is. It has nor really changed over the years.
"It's the combination of a strong economy, a good society, good public services that can help people, protection for people on the streets.
"These things are what I stand for."
He added that the Conservatives had called Brexit under "false pretences", claiming they can "get Brexit done".
"The truth is, even if 650 Tory MPs are elected it still wouldn't be done. It will go on for some time in the future."
See Monday's Express & Star for an exclusive interview with Mr Blair, in which he discusses Brexit and his fear of a Tory government.
The other candidates for Wolverhampton South East are Conservative Ahmed Ejaz, Raj Chaggar of the Brexit Party, Lib Dem Ruth Coleman-Taylor and the Green Party's Kathryn Gilbert.