He was educated at Amenia Seminary, and graduated from Yale College in 1841.

Then he studied law, was admitted to the bar, and commenced practice in Poughkeepsie in 1844.

Dean was elected as a Democrat to the 32nd and 33rd United States Congresses, and served from March 4, 1851, to July 3, 1854, when he resigned.

He was appointed a justice of the New York Supreme Court (2nd District) on June 26, 1854, to fill the vacancy caused by the death of Seward Barculo, and remained on the bench until the end of 1855, being ex officio a judge of the New York Court of Appeals in 1855.

He died on October 12, 1870, and was buried at the Presbyterian Cemetery in Pleasant Valley.