In 1878, William N. Davidson moved to Luverne, the seat of Rock County in southwestern Minnesota. There he practiced law, served as attorney for the city and county, and was county surveyor for thirty years.
In 1892, he was nominated by the Peoples Party for Associate Justice of the Minnesota Supreme Court. This was the era of fusion politics, when a minor party such as the Peoples, also known as the Populist Party, endorsed candidates nominated by a major party to give that man an edge on election day. In 1892 the Peoples Party also endorsed Democrats Daniel Buck and Thomas Canty, who with William Mitchell, were elected. Davidson was the sole candidate for the Court with only one endorsement, and came in last in a field of six.
He died on August 23, 1920, at age eighty-six. In an obituary, the local newspaper recalled him:
"[H]e was in an unusually deep student [of the law] and possessed a marvelous memory, and his judgment on points of law was frequently sought and greatly valued by members of the profession over a wide area.
"He was truly a lawyer of the old-school, conservative and sound in his judgment, with a generosity of heart that seldom permitted him to exact for services rendered anywhere near their actual worth."