Barry was born in Itta Bena, Mississippi. He grew up in Memphis, Tennessee and graduated from LeMoyne College there. In 1958, he joined the American civil rights movement during a movement to eliminate racial segregation of bus passengers, and was elected the first chairman of the Student Nonviolent Coordinating Committee. He abandoned his graduate chemistry studies at Fink University in Nashville, Tennessee, from whom he had recieved a Master's Degree, for his new duties. During his time leading the Committee, Barry heavily lobbied against racial segregation and discrimination.

In 1965, Barry moved to Washington, DC to open a local chapter of the Student Nonviolent Coordinating Committee, where he was heavily involved in coordinating peaceful street demonstrations, until the 1970s, when he became involved in politics.

Whilst serving on the city council in 1977, Barry was shot attempting to defend the District Building, threatened by radical Black Muslim terrorists. Barry was shot near his heart during a two-day crisis in which hostages were held by the terrorists, and which was finally defused by the FBI, and Muslim ambassadors.

He served on the first city school board to implement school board elections, in 1971, and served as Board president during his tenure. He was elected a member of Washington's first elected city council in 1974, and whilst serving as a council member, became chair of the Committee on Finance and Review. In 1978, Barry was elected mayor of Washington, DC. He was only the second person elected to this position. Barry held this position for 12 years, until he was arrested by police in 1990 for a misdemeanor crack cocaine conviction.

As a result of his arrest and ensuing trial, Barry was forced to step down from his position, and was sentenced to a six-month federal prison term in October 1990, during his campaign for a District Council seat. After being released from prison, Barry was successful in his bid for a Council seat in 1992. In 1994, Barry again claimed the position of Mayor, which he held until January 1999, at which time he handed the position to Anthony A. Williams, his former CFO.

From 1997 onwards, the D.C. Funding Board reduced the power which Barry had been given to allocate and manage funds for city projects. The Mayor was also involved in further unsubstantiated public scandals, eventually leading to his decision not to run for a fifth term in office.

(Not to be confused with Marion Berry, U.S. Representative from Arkansas.)