in 1818 pettus arrived in st. louis from virginia where he served in the war of 1812. while a land office clerk in st. louis, he was elected secretary of the state convention which wrote the missouri constitution when it was admitted into the united states in 1821. his public service included secretary of state in the alexander mcnair administration, probate judge of st. louis county and in 1832 he was elected a member of the state senate for the st. charles district.