 He moved to Iowa in 1844, attended the University of Iowa, studied law and was admitted to the bar in 1847, commencing practice in Marion, Iowa.Smyth served as prosecuting attorney of Linn County, Iowa from 1848 to 1853 and was appointed judge of the district court for the fourth judicial district of Iowa in 1853, serving until 1857.He resumed practicing law and in 1858 served as chairman of the commission to codify and revise the Iowa State laws.