In 1844, Parker moved to Albany to begin serving as a judge of the New York State Circuit Court, a position he held until 1847. Parker became a justice of the New York Supreme Court in 1847, and served until 1855. In 1854, Parker served as an ex officio judge on the New York Court of Appeals. After leaving the bench, he again resumed the practice of law. Parker was a founder of Albany Law School in 1851, and was the unsuccessful Democratic nominee for governor in 1856 and 1858. In 1867-68 he was a delegate to the state constitutional convention.