He was born in Vinton, Iowa on October 6, 1859 to George W & Elizabeth [Hedden] Sells. His father died when he was 13 years of age and young Cato was need to help support his family. He secured employment as a clerk in a hardware store for three years in La Porte, Iowa. The owner allowed Cato to attend school during the winter months without the loss of wages. He entered Cornell College in Mt. Vernon Iowa in 1875 where he helped support himself as a superintendent of the boarding hall. In 1878 he returned to La Porte and began studying lawy under Judge Charles Alvord Bishop and in 1880 was admitted to Iowa State Bar Association and began practice at La Porte City, Iowa. In 1887 he was chairman of the committee and was a delegate to the 1888 Democratic National Convention. In 1889 he moved to Vinton, Iowa and served on the Iowa State Central Committee. He married Lola A. McDaniel in 1891. They had three children: Dorothy, Donald and Barbara Leigh. He was a delegate to the 1892 Democratic National Convention as secretary. In 1892 he was elected as a trustee of the Iowa State College of Agriculture. In 1893 he was president of the Iowa Democratic State Convention. In 1894 he was appointed by Grover Cleveland as United States Attorney for the United States District Court for the Northern District of Iowa. In 1899 he was again president of the Iowa Democratic State Convention and in 1900 chairman of the Iowa delegation in the 1900 Democratic National Convention in Kansas City.

He was a commissioner at the Bureau of Indian Affairs from 1913 from 1921. In 1914 he banished books that taught anything concerning the Asian origins of Indigenous peoples of the Americas.

The settlement of Sells, AZ took its present English name in 1918 to honor Indian Commissioner Cato Sells.