His father, William Sanford Pennington was a Revolutionary War veteran and was himself Governor of New Jersey from 1813 to 1815 before President Madison appointed him as a federal judge.

His tenure as governor was marked by the "Broad Seal War" controversy.

Following a disputed election for Congressional Representatives in New Jersey, Pennington certified the election of five Whig candidates while five Democrats were certified by the Democratic Secretary of State.

[2] It was the second time since 1789 that the House elected a freshman congressman as its speaker (after Henry Clay in 1811[a]); the feat has not been repeated since.

[4] After running unsuccessfully for reelection in 1860 to the 37th Congress, he returned to New Jersey, dying in Newark of an unintentional morphine overdose.