He served as Attorney-General of Pennsylvania and United States Postmaster General[1][2] during the presidency of Franklin Pierce.

After the state's constitution was amended in 1850 to allow elected judges, he was nominated for the Supreme Court, at a period when Know-Nothingism and anti-Catholic feeling was rife.

[3] James Buchanan remarked to a friend in Pennsylvania, "It would be a sad affair for the party, should Campbell fail & the remainder of the Judicial ticket be elected.

Campbell's Cabinet service was a reward to the faction of the Democratic Party that supported James Buchanan in the 1852 presidential nomination convention.

In 1873 he was elected a member of the Constitutional Convention of Pennsylvania, but declined to serve, owing to the condition of his health.

He made visits almost daily to St. Joseph's Orphan Asylum, to Girard College, and to the hospital, examining conditions in detail, and considering them with as much care as if they referred to his own life or to the lives of those of his own household.