After the war, Ashley became a merchant and performed some surveying. Ashley was then elected as Missouri's first Lieutenant Governor in 1820 and served until 1824.

I call Ashley 'the reluctant adventurer'. According to Don Berry, in his book, A Majority of Scoundrels, he states that Ashley's first love and focus was politics (served as a U.S. Representative for the Jacksonian party between 1831 to 1837) and he wanted to become the governor of the state. But, then as now, politics requires money, so Ashley turned to the fur business as a source of revenue to support his run for the governorship.

In 1822, William Ashley & Andrew Henry began posting the now famous ads seeking the 100 enterprising young men to ascend the Missouri River to its source. Ashley was the businessman behind the operations while Henry was the field commander. Henry had knowledge of the fur business and had been to the Snake River area in 1811.