was a regional field director in Iowa for Al Gore’s 2000 presidential campaign, worked at the Democratic Senatorial Campaign Committee in 2004, and was the national political director at the Democratic Congressional Campaign Committee in 2005 when then-Representative Rahm Emanuel led the group’s efforts to reclaim a congressional majority.

He worked on grassroots efforts for Mr. Obama in New Hampshire and South Carolina during the primaries in 2008, and later in Michigan and Pennsylvania during the general election. He went on to found the group New Partners Consulting with Obama campaign alumni.

In a statement, Mr. O’Malley, who has been modeling his himself as an insurgent outsider, called Mr. Hamrick the “perfect choice.”

“He brings a tremendous amount of political experience and a strong grasp for Iowa politics,” Mr. O’Malley, whose hopes are banking heavily on beating expectations in the caucuses state, said. “Plus, he shares my admiration for our nation’s poet laureate, Bruce Springsteen, and has seen him in concert more than 50 times.”