Sardins Mason Brewster was born in Irving Township, Brown County, Kansas, on June 19, 1870. When he was about four years of age his parents moved to White Cloud, Doniphan County, Kansas, where he resided for more than thirty years. His father was Arthur Seeley Brewster, a native of New York, who came with his parents to Ashtabuia County, Ohio, at an early age. His father was a practicing attorney at White Cloud and practiced in Doniphan, Brown and neighboring counties. He was for six years county attorney of Doniphan County, Kansas, and held many positions of public trust. He was a graduate of the Albany Law School. He died December 24, 1905.
Sardins Mason Brewster was admitted to practice law in Doniphan County in 1897. In 1898 he was elected county attorney of Doniphan County, Kansas, taking office in 1899. He served five consecutive terms of two years each. In 1908 he was elected to the State Senate from the First Senatorial Distriet, consisting of Brown and Doniphan counties and served in the sessious of 1909 and 1911. In 1911 he was appointed assistant attorney-general of the State of Kansas by Attorney-General John S. Dawson and served in that position until January, 1915. In 1913 he was elected as a member of the House of Representatives from Doniphan County, Kansas, and served in the Legislature of 1913. In 1914 he received the Republican nomination for attorney-general of Kansas and was elected to that office, taking office in January, 1915. In 1916, he was renominated by the republicans for the office of attorney-general and was ro-elected.
He was married on February 1, 1899, to Caroline Brown of Emporia, Kansas. They have five children living.