In 1872, Watson was elected to the Oregon State Senate as a Republican from Douglas County.[2] He won re-election in 1874 to the same seat in the senate.[3] Next, in 1876 Watson won election to the Oregon Supreme Court to replace John Burnett.[4] His term ended in 1878 and he left the bench, however, his younger brother Edward B. Watson would join the court in 1880.[4][4]