Born in Bradford, he attended the common schools and Kimball Union Academy (Meriden, New Hampshire).

Wadleigh served six terms as town moderator and was a member of the New Hampshire House of Representatives in 1855-1856, 1859-1860, and from 1869 to 1872.

Wadleigh was nominated to the U.S. Senate on the evening of June 13, 1872 by the Republican party caucus of the New Hampshire legislature, on its fifth ballot.

Charles H. Bell was Wadleigh's immediate successor, and had been appointed to fill the Senate seat for several months, until the most recently elected New Hampshire legislature could convene.

He resumed the practice of law in Boston, where he died in 1891; interment was in West Street Cemetery, Milford.