Toward the close of the same year, he was appointed Attorney General for the new State of Missouri, and in 1826, while yet a young man, was elected representative to congress as an anti-Democrat, and served one term.
For the following twenty-five years, he devoted himself to his profession, in which he was a shining light.

His probity and uprightness attracted to him a class of people who were in the right and only sought justice, while he repelled, by his virtues, those who traffic in the miseries or mistakes of unfortunate people, for they dared not come to him and seek counsel to aid them in their villainy.
In 1847, Mr.Bates was delegate to the Convention for Internal Improvement, held in Chicago, and by his action he came prominently before the whole country.

In 1850, President Fillmore offered him the portfolio of Secretary of War, which he declined.

Three years later, he accepted the office of Judge of St.Louis Land Court.
When the question of the repeal of the Missouri Compromise was agitated, he earnestly opposed it, and thus became identified with the "free labor" party in Missouri, and united with it, in opposition to the admission of Kansas under the Lecompton Constitution.

He afterwards became a prominent anti-slavery man, and in 1859 was mentioned as a candidate for the presidency.