Brown moved to Roswell, New Mexico in 1910 and became the football coach and athletic director at the New Mexico Military Institute. In his first year as the head coach at NMMI, he led the team to a 2–0 record with wins over New Mexico State (5–0) and New Mexico (80–0). He also led the team to undefeated records in 1912, 1916, 1917, and 1919. Players from his 1912 team were selected for four of the eleven spots on the 1912 All-Southwestern Eleven. In a historical account of that institution's football program, Brown is credited with the development of the program: "Gradually, football got under way and with the arrival of Mr. R.R. Brown and professional, precision coaching in 1910, interest in the sport boomed and regional success followed." With the exception of a brief period when he coached at New Mexico College of Agriculture, Brown remained the head coach at the New Mexico Military Institute until at least 1937.
As of 1918, Brown was also employed as a bank clerk at the First National Bank in Roswell. In a passport application filed that same year, he identified his profession as an athletic director and teacher. During World War I, he traveled to France for one year as part of a Y.M.C.A. service.
At the time of the 1930 U.S. Census, Brown was still living in Roswell, New Mexico, where he was employed as a teacher at the state school. Brown died on December 24, 1950 in Roswell. He had retired from his position as athletic director at the New Mexico Military Institute in 1948.
^ abU.S. Passport Application for Robert Roswell Brown dated September 4, 1918. The application stated that Brown was unmarried and was born in Joliet, Illinois on November 28, 1879. The application identifies his father as Roswell Stuart Brown, deceased. National Archives and Records Administration (NARA); Washington D.C.; Passport Applications, January 2, 1906 - March 31, 1925; Collection Number: ARC Identifier 583830 / MLR Number A1 534; NARA Series: M1490; Roll #: 640. Ancestry.com. U.S. Passport Applications, 1795-1925 [database on-line].
^"Rockne Names New Mexico Coach as Aid in Southwest". Daily Las Vegas Optic. April 13, 1928. p. 4.("Capt. Brown is a popular figure in athletic activities in this area and has been a prominent factor in football for mere than twenty years. He has been head coach of football at Tulane, Virginia Poly, the University of North Carolina and at Washington and Lee. He has been at the Military Institute since 1910 and since then has won the championship of the Southwestern Conference several times. Brown was a star halfback and full back at Dartmouth in 1900 and 1901.")
^World War I Draft Registration Card dated September 1918 for Robert Roswell Brown, born November 28, 1879. Registration State: New Mexico; Registration County: Chaves; Roll: 1711858. Ancestry.com. U.S., World War I Draft Registration Cards, 1917-1918 [database on-line].
^Census record for Robert Roswell Brown, age 50, born in Illinois. Ancestry.com. 1930 United States Federal Census [database on-line]. Year: 1930; Census Place: Roswell, Chaves, New Mexico; Roll: 1393; Page: 18A; Enumeration District: 2; Image: 81.0; FHL microfilm: 2341128.