Father Mortimer Augustine Sullivan was born in Lawrence, Massachusetts, on 2 January 1887. He entered the Augustinian novitiate at Villanova, Pennsylvania in 1904 and two years later went to Rome to study at the International College of Saint Monica. He was ordained to the priesthood in Rome in 1909.

After ordination Father Sullivan returned to the United States where he served as an assistant at Saint Laurence's parish in Lawrence, Massachusetts; at Saint Rita's in Philadelphia, Pennsylvania, and at Immaculate Conception in Hoosick Falls, New York. From 1914 to 1917 he was a member of the Augustinian mission band. He also served as a chaplain in the United States Navy during the First World War.

After the War, Father Sullivan served as an assistant at Saint Nicholas of Tolentine in Atlantic City, New Jersey. In 1925 he was named President of Villanova College. The following year he was appointed Prior and Pastor at Saint Matthew's in Flint, Michigan. He held the same office at Saint Nicholas of Tolentine in Jamaica, New York, in 1929.

At the Chapter of 1932 Father Sullivan was elected Prior Provincial of the Province of Saint Thomas of Villanova. After serving two terms in this office, he became Prior and Pastor at Saint Nicholas of Tolentine in Atlantic City, New Jersey. He served again as Provincial from 1944 to 1949. During his last term as Provincial, Merrimack College in Andover, Massachusetts, was established, and negotiations were proceeding for the opening of Carroll High School, Washington, D.C.

Father Sullivan was 62 when he died in Atlantic City Hospital, Atlantic City, New Jersey, on 13 July 1949. He is buried in the Augustinian Community plot of the Saint Mary's cemetery in Lawrence, Massachusetts.

Two buildings are named in Father Sullivan's honor: the Liberal Arts building at Merrimack College, Andover, Massachusetts, and Sullivan Hall on the Villanova University campus.