John Barry Mahool (September 14, 1870 – July 29, 1935) was the Mayor of Baltimore from 1907 to 1911.

Mahool was born in Phoenix, Maryland on September 14, 1870.^[1] He became the Democratic nominee for Baltimore mayor in April 1907, defeating opponents John Charles Linthicum and George Stewart Brown. In May 1907, he defeated incumbent Republican mayor E. Clay Timanus.^[2]

In 1910, Mahool signed city ordinance No. 610 prohibiting African-Americans from moving onto blocks where whites were the majority, and vice versa.^[3] Mahool had been an advocate for social justice, championing causes such as woman's suffrage, but the ordinance came in response to an uproar after George W. F. McMechen, an African-American Yale law school graduate, moved into a rich (white) neighborhood. The ordinance was rapidly declared unconstitutional.^[4]

Mahool lost a re-election bid in 1911 in the primary, losing to James H. Preston.^[5][6]

Mahool died in Baltimore on July 29, 1935, nine days after suffering a fall in Ocean City, Maryland.^[7]