Acting Mayor Kim Janey gained the political backing of former City Councilor Tito Jackson Tuesday, Janey's predecessor on the council and the last challenger to go up against an incumbent mayor in the city's general election.

In a statement from Janey's mayoral campaign, Jackson mentioned Janey's work on social, racial, economic, educational and environmental justice issues throughout her career as an activist and politician.

"She knows the challenges residents of Boston face every day because she has faced them herself," Jackson said.

Jackson gave up his District 7 City Council seat to mount an unsuccessful challenge to then-Mayor Marty Walsh in 2017. Janey won the race to replace him.

Jackson promised that Janey will "create more affordable housing and paths to homeownership, make sure our public transportation system works for the riders who depend on it every day and ensure equity and excellence for every student in the Boston Public Schools," if she receives a full term.

He said the most pressing issue of all is Janey's work supporting communities hardest hit by the COVID-19 pandemic with access to vaccines and financial support.

Janey and Jackson plan to canvass together Thursday.

After leaving office, Jackson became CEO and owner of medical and recreational cannabis company Verdant Medical.

A coalition of Black Bostonians trying to unite Black support behind one candidate endorsed Janey last week. The group, known as WAKANDA II, scored the candidates based on interviews, forums and questionnaires before deciding on Janey. The acting mayor also picked up the support of service employees labor union 32BJ SEIU.

Another leader of Boston's communities of color, former State Representative Marie St. Fleur, endorsed City Councilor Andrea Campbell in May.

UMass Boston political science professor Erin O'Brien told GBH News that even though Jackson fell short of unseating Walsh four years ago, his support still carries weight as the large field of candidates comes closer to the Sept. 14 preliminary election.

"There are a significant number of voters who really like Tito Jackson and then probably have a number of candidates in the current mayoral primary that they like. So getting a signal from Tito Jackson, someone who was willing to challenge the establishment, is a big deal," O'Brien said.

In 2017, Jackson beat Walsh with over 60% of the final vote in Roxbury's Ward 12 and with over 57% of the vote in Ward 11, the only two wards the challenger won.

O'Brien said Jackson's endorsement could help progressive voters decide to support Janey over her closest competition in the polls, At-Large City Councilor Michelle Wu.

"The reality of this race is it's Wu and Janey, and of those two, Tito Jackson chose to have his voice heard and who he prefers," O'Brien said.