Elijah was the son of Major Moses Porter, who fought in the Revolutionary War, and Sarah Killam, a direct descendant of Captain Miles Standish.

In 1846, Porter passed the New York Bar, ranked high among its leadership, and was admitted to practiced law before the State's Supreme Court.

[2] In early 1865, Porter was appointed to the New York Court of Appeals to fill the vacancy caused by the resignation of Henry R. Selden.

In November 1865, he was elected on the Republican ticket to the remaining six years of Selden's term, but resigned on December 31, 1867, and returned to private practice in New York City.

In February 1876, Porter defended Grant's military secretary Orville E. Babcock, who had been indicted during prosecution of the Whiskey Ring frauds.