He traveled to Oregon Country as a secular member of the Methodist mission, where he became involved in politics and helped found the first American newspaper west of the Rocky Mountains.

[1] He, his wife, and two children joined the Great Reinforcement that sailed on the ship Lausanne around Cape Horn to the Pacific Northwest.

[4] On June 3, 1845, Abernethy was elected to serve as Provisional Governor of the Oregon Country, defeating Osborne Russell, a member of the outgoing Executive Committee.

Abernethy and his supporters were American loyalists who believed that the Provisional Government was strictly interim until the question of U.S. and British claims on the Oregon Country were finalized.

He and eight other leading citizens established the Oregon Exchange Company, which became the de facto territorial mint for a short time.

Several other public works (and natural features such as streams) in Oregon are also named in his honor; though several are given the variant spelling of Abernathy.