Rob Garagiola, the Democratic majority leader of Maryland's state Senate, will formally announce his run for the House against Rep. Roscoe Bartlett (R-Md.).
Garagiola is expected to be the front-runner in the Democratic primary to unseat Bartlett, who has held the seat for 20 years. Bartlett's district was redrawn during redistricting and is now more competitive territory for Democrats.
Garagiola had already started building momentum for his campaign before he officially declared he would run. Last week, he announced endorsements from almost 20 state senators and delegates, The Baltimore Sun reported.
A former Army sergeant, Garagiola will officially announce his campaign on Tuesday during four events in the district.
Bartlett won his last reelection in 2010 by almost a 30-point margin over Democrat Andrew Duck. Bartlett, 85, is the second-oldest member of the House.
Duchy Trachtenberg, a former county council member, is also running in the Democratic primary.