The Democratic field to succeed retiring Rep. Bill Delahunt (D-Mass.) began shaking out within hours of his making his retirement official on Friday.

State Sen. Robert O’Leary (D) confirmed to local news outlets Friday that he would run for Delahunt’s 10th district seat, and he is expected to be joined by Norfolk District Attorney William Keating. They are considered the most high-profile in a larger crop of Democratic candidates eyeing the race.

State House Assistant Majority Leader Ronald Mariano (D) also confirmed Friday that he is mulling a bid.

State Rep. James Murphy (D) and Ian Bowles (D), secretary of Massachusetts’ Executive Office of Energy and Environmental Affairs, did not immediately respond to requests for comment.

Insurance executive Phil Edmundson (D), meanwhile, ruled out a campaign on Friday.

State Rep. Jeffrey Perry and former state Treasurer Joe Malone are the leading contenders on the Republican side.