After resigning as Chancellor in 1843, Governor John S. Barry appointed Farnsworth as Attorney General, a position which he held for two years.

He was appointed to the board by the Governor in 1846 and served in that capacity until 1852 (while simultaneously being an ex officio member as Chancellor from 1846 to 1847).

He was influential in the board's selection of Henry Philip Tappan as the first President of the University of Michigan.

He was a Director of the Michigan Central Railroad and President of the Detroit Savings Bank from 1849 until shortly before his death.

He died March 24, 1877, of complications from a long-term kidney disease and is buried at Elmwood Cemetery.