[2][1] In 1994 he sought the United States House of Representatives seat in Massachusetts's 3rd congressional district.

He ran as a moderate "New Democrat" and a D.C. outsider against longtime Congressional aide and the more liberal Jim McGovern.

[2] He defeated McGovern 38% to 30% in the Democratic primary, but lost the general election to Republican incumbent Peter Blute 55% to 44.

[4] This included promoting the city's convention center, which saw bookings 160% ahead of projections during O'Sullivan's tenure, and pitching Worcester Regional Airport to airlines.

In 1998, he became the vice president of the Massachusetts Biomedical Initiatives, a non-profit that runs business incubators in Worcester.