During the transitional period following 1890, the LDS Church disbanded its People's Party, "and the Saints were encouraged to align themselves with the national parties." Roberts became a fervent Democrat and was elected Davis County Delegate to the Utah State Constitutional Convention in 1894. Roberts proved a vocal member of the Convention, particularly in his opposition to women's suffrage.  In 1895, Roberts was the losing Democratic candidate for the U.S. House of Representatives, and Roberts believed LDS Church leaders, who were predominantly Republicans, "had unfairly influenced the election by publicly reprimanding him and fellow Democrat Moses Thatcher for running for office without express permission of the Church." The LDS Church then issued the "Political Manifesto of 1895," which forbade church officers from running for public office without the approval of the church. Both Roberts and Thatcher refused to agree to the Political Manifesto and were suspended from their ecclesiastical offices. Roberts, believing such a requirement was a basic infringement of his civil rights, capitulated just hours before a deadline of March 24, 1896, signed the manifesto, wrote a letter of apology to the First Presidency, and was reinstated. Thatcher was more stubborn: he refused to sign, was expelled from the Quorum of the Twelve Apostles and barely evaded excommunication. In 1898, Roberts was elected as a Democrat to the 56th Congress, but the House of Representatives refused to seat him because of his practice of polygamy. The prolonged battle that ensued to keep his seat, which was not successful, left Roberts bitter.  The governor of Utah had appointed Roberts a chaplain in the Utah National Guard; in 1917, when the United States declared war on Germany, Roberts volunteered to serve as a U.S. Army chaplain. The age limit of forty was waived--Roberts was then sixty--and Roberts became chaplain to the 145th Field Artillery, which arrived in France in September 1918 but did not see action before the Armistice was signed in November.

Answer this question "How did he start his political career?" by extracting the answer from the text above.
Roberts became a fervent Democrat and was elected Davis County Delegate to the Utah State Constitutional Convention in 1894.