Born in Baltimore, Maryland on October 25, 1795, Kennedy graduated from Baltimore College in 1812 and fought in the Battles of Bladensburg and North Point in the War of 1812. Although admitted to the bar in 1816, he was much more interested in literature and politics than law. He published Swallow Barn in 1832 and Horseshoe Robinson in 1835 to win a permanent place of respect in the history of American fiction.

Kennedy was an active Whig, winning a seat in the Maryland House of Delegates in 1820. In 1838 he succeeded Isaac McKim in the U.S. House of Representatives but was defeated in his bid for reelection in November of that year. He was re-elected to Congress in 1840 and 1842; but, because of his strong opposition to the annexation of Texas, he was defeated in 1844. His influence in Congress was largely responsible for the appropriation of $30,000 to test Samuel Morse's telegraph.

President Millard Fillmore appointed Kennedy to the post of Secretary of the Navy in July 1852. During Kennedy's tenure in office, the Navy organized four important naval expeditions including that which sent Commodore Matthew C. Perry to Japan.

Kennedy retired from public life in March 1853 when President Fillmore left office, but he retained an active interest in politics and forcefully supported the Union. At the end of the American Civil War he advocated amnesty for the South. He died at Newport, R.I. in 1870, and is buried in Greenmount Cemetery in Baltimore, Maryland.

USS John P. Kennedy and USS Kennedy (DD-306) were named for him.

This article includes public domain text from the Naval Historical Center.