Sean M. O'Brien is a fourth-generation Teamster, initiated in 1991 working in the Rigging Industry. Since 1999, Sean has held nearly all positions for Teamsters Local 25.

In 2006, Sean became the youngest President in Local 25's long history. Teamsters Local 25 represents more than 11,500 members and their families in Greater Boston. In 2011, Sean was elected Eastern Region International Vice President of the International Brotherhood of Teamsters. Sean also serves as Secretary-Treasurer of New England Joint Council 10.

O'Brien has worked tirelessly to increase the membership of the Teamsters both locally and nationally and has been successful in organizing various diverse industries. Sean serves as a Trustee on both the New England Teamsters Pension Plan and the Local 25 Health Insurance Plan where he has skillfully negotiated the growth of both plans over the last five years.