McClelland became a member of the Michigan bar and established a successful law practice in Monroe, and he was a member of the constitutional convention in 1835. After Michigan became a state, Governor
Stevens T. Mason offered the positions of state Bank Commissioner and state
Attorney General, both of which he declined in order to develop his private practice, although he maintained an active role in the new state's
Democratic Party. McClelland served on the board of regents of the
University of Michigan in 1837 and again in 1850. He represented
Monroe County in the
Michigan House of Representatives in 1838, 1840 and was speaker of the house in 1843. He served as the mayor of Monroe in 1841. He was elected in 1842 as
U.S. Representative from
Michigan's 1st congressional district, serving from 1843 to 1849 in the
28th,
29th, and
30th congresses. Going against the general opinion of the Democratic Party, he was a strong advocate of the
Wilmot Proviso, which would have restricted the spread of slavery to new states. He was active in supporting his friend
Lewis Cass's unsuccessful run for president in 1848 and did not seek reelection in that year. McClelland played a prominent role in the Michigan's constitutional convention of 1850. Due to changes adopted in that constitution, he was elected to a one-year term as
Governor of Michigan in 1851. He was re-elected to a full two-year term in 1852. During his tenure, he softened his support of the Wilmot Proviso and instead urged support for the
Compromise of 1850. He played a prominent role at the national Democratic convention of 1852. He resigned as governor in March 1853 to become the
Secretary of the Interior under
Franklin Pierce, and was succeeded by his second Lieutenant Governor
Andrew Parsons. ==Retirement and death==