John Power Knowles (June 13, 1808 – August 3, 1887) was a United States federal judge.
Born in Providence, Rhode Island, Knowles received an AB from Brown University in 1836 and an LL.B. from Harvard University in 1838. He was in private practice in Providence, Rhode Island from 1838 to 1855. He was a member of the Rhode Island General Assembly in 1855. He was a Court reporter, Providence, Rhode Island from 1855 to 1857. He was in private practice in Providence, Rhode Island from 1857 to 1865. He was a Court reporter, Providence, Rhode, Island from 1865 to 1866. He was a member of the Rhode Island General Assembly in 1866. He was a City solicitor, Providence, Rhode Island from 1866 to 1867. He was in private practice in Providence, Rhode Island from 1867 to 1869.
Knowles was a federal judge on the United States District Court for the District of Rhode Island. Knowles received a recess appointment from Ulysses Grant on October 9, 1869, to a seat vacated by Jonathan R. Bullock. Formally nominated on December 6, 1869. He was confirmed by the United States Senate on January 24, 1870, and received his commission the same day. Knowles served in that capacity until March 21, 1881, due to retirement.
He died in Providence, Rhode Island.