Born in Worcester, Massachusetts, O'Toole received a Bachelor of Arts from Boston College in 1969 and a Juris Doctor from Harvard Law School in 1972.

5089 following the appointment of Rya W. Zobel as director of the Federal Judicial Center.

O'Toole presided over the 2015 trial of Dzhokhar Tsarnaev, one of the perpetrators of the Boston Marathon bombing.

[2][3] On February 6, 2025, O'Toole temporarily blocked the U.S. federal deferred resignation program.

[5] He is married to Lucy A. Flynn, a local banker, businesswoman,[6] and community activist.