Boston City Councilor Tito Jackson, perhaps Mayor Marty Walsh’s most persistent critic, is taking the plunge and will seek to replace Walsh as the city’s chief executive.

The conventional wisdom among political professionals is that it will be an uphill fight.  Not since 1949 has an incumbent mayor lost a reelection bid

Walsh beat City Councilor John Connolly for the mayoralty in 2013, winning by 3.49 percent – the narrowest margin of victory in recent memory.

Since then, however, Walsh has solidified his position. He enjoys high poll ratings and has a political war chest worth $3.5 million and growing.

At the beginning of this month, the 41-year-old Jackson had not quite $65,000.

Jackson released a video Wednesday introducing himself to voters and making a case that income inequality and the issues that stem from it – such as substandard education and inadequate neighborhood safety – should be the top issues of this campaign.

Walsh and Jackson have clashed on the failed bid to bring the Olympics to Boston and levels of funding for the Boston public schools.

Jackson is expected to formally announce his candidacy Thursday at 2 o'clock at Roxbury's Haley House, a nonprofit cafe and service center.