[2] Mason was admitted to the Suffolk County bar in 1843 and began practicing in Boston.

As a member of the board, Mason was influential in the establishment of the State Normal School at Framingham.

In the House he was a leading proponent of the leveling of Boston's Fort Hill, the merger of the Western Railroad and the Boston and Worcester Railroad, and the adoption of the Fourteenth Amendment to the United States Constitution.

[1] On December 22, 1870, he was appointed United States Attorney for the District of Massachusetts by President Ulysses S.

[4] They had five children:[4] He was a distant relative of Rufus Osgood Mason, who also grew up in Sullivan, New Hampshire.