Pendleton was a delegate to every Democratic State convention from 1876 to 1910. Pendleton was selected as state representative of the Twenty-fourth District, which included Bell County, and retained office for the Eighteenth, Nineteenth, and Twentieth legislatures; he served as Speaker of the House in 1887–1889. Between 1883 and 1889, while a member of the state legislature, he held a number of positions within the state's Democratic Party, including chairman pro tem of both the antiprohibition state convention of May 1887 and the state convention in 1888. The 1890 Democratic state convention, cognizant of Pendleton's Granger past, nominated him as gubernatorial candidate James S. Hogg's running mate on a platform designed to appeal to the state's agrarian voters during this period of farmer activism. Following Hogg's victory Pendleton served as Lieutenant Governor of Texas from 1891 through 1893 under Governor James S. Hogg. In 1892 he successfully sought election to Congress from the state's Seventh District, which included Bell, Falls, McLennan, Freestone, Limestone, Milam, Brazos, and Robertson counties. He served two terms in Washington and was a delegate to the Democratic National Convention in Chicago in 1896.