John Richard Slattery (July 16, 1851 – March 6, 1926) was an American former Catholic priest, activist, missionary, writer, and lawyer.

He was first a member of the Mill Hill Missionaries, later becoming in 1893 a co-founder and the first superior general of the Society of St. Joseph of the Sacred Heart (also known as the Josephites).

His work in both religious communities was with African Americans in the aftermath of the Civil War and Reconstruction, a mission first inaugurated by the Mill Hill founder, Cardinal Herbert Vaughan, in 1871.

[2][3][4] Slattery worked for years in the mission field, establishing parishes, schools, and other ministries on behalf of the society.

A lawyer by trade from then until his death on March 6, 1926, his fortune and papers were left to the New York Public Library.