In 1822, David returned to England and convinced William to join him in America. William remained with David until the spring of 1825, when he joined a caravan to New Mexico. In July, he checked in at the customs house in Santa Fe and later settled in San Francisco del Rancho, a community south of Taos. It was in the Taos area that Workman began his involvement in fur trapping, distilling, and the operation of a store, with partner John Rowland. Workman was baptized a Catholic in 1828, became a naturalized Mexican citizen, and married Nicolasa Urioste, a Taos native.
Workman seems to have made a good living in Taos, but politics soon made life difficult.
In 1840 the Republic of Texas named Workman and Rowland agents, perhaps without their prior knowledge, to represent Texas' interests in annexing New Mexico. Although they did not apparently accept this role, Workman and Rowland's identification with the Texans was tantamount to treason. As tensions increased and the Texans began to march for Santa Fe, Rowland and Workman formed a party of some forty whites that left New Mexico in September 1841. Taking in about 25 New Mexicans shortly after leaving, the party traveled the Old Spanish Trail , arriving in Los Angeles on 5 November 1841. The Rowland and Workman expedition left its legacy as the first emigrant party to enter southern California from an eastern-based land route.