Returning to Mississippi, he married Mariah Louise Bates of Holmes County, Mississippi, on January 14, 1874, and he returned again in 1875 to Marietta to join his brother Jim at the fledgling chair factory. He and Jim became partners in Brumby and Brother in 1875, and in 1878 he moved his wife and infant son, Tom, Jr. to Marietta.

In 1884, Thomas and Jim incorporated the chair factory as Brumby Chair Co. In 1888, Thomas Micajah Brumby bought out his older brother Jim, who was retiring due to poor health and succeeded him as president of the Brumby Chair Co., a position he held until he retired because of his own poor health in 1923. During his almost one-half century stewardship of the Brumby Chair Co., it became one of the largest chair factories in the South and one of Marietta's major employers. One newspaper columnist wrote: "Brumby chairs became as distinctive in their own province as Chippendales and Hepplewhites."

He was twice elected mayor (1898-99 and 1900-1901) but modestly declined to serve a second term. He helped organize and was president of the Marietta Electric Co., which was the forerunner of the present Marietta Board of Lights and Water. In business affairs, he and James T. Anderson, R.H. Northcutt and Newt Adams organized Marietta Bank and Trust Co.

A lifelong Methodist, he was chairman of the building committee which built the First Methodist Church at the comer of Atlanta and Anderson streets in 1899. He was also chairman of the Marietta School Board for several years and served in this capacity when Waterman Street School, Marietta's first school building, was built.

At the time of his death, March 1, 1925, the Cobb County Times eulogized him as a "strong political factor in both state and county politics . . . his support was ardently sought by all those who aspired to public office and he lent his hardy support to those who represented clean, honest government. He was a man with strong convictions, fearless and an avowed enemy of corruption and lawlessness. He was a man whose purpose could never be questioned . . . he achieved success in a truly impressive manner; his famous product the Brumby porch rocker, being found in nearly every Southern home."

In addition to following his older brother Jim to Marietta from rural Mississippi in the aftermath of the Civil War, Thomas M. "Pappy" Brumby eventually bought and reared his family in the Victorian house on Kennesaw Avenue built by his brother, Jim, in 1882 before he retired to Florida in 1888. In the Kennesaw Avenue house in the shadow of the chair factory, "Pappy" Brumby and Mariah Bates his wife of 49 years, reared their six sons and one daughter, Mariah (Mrs. George Sessions).

Mrs. Brumby, an active member of The First Methodist Church, was known to friends as a self-sacrificing Southern lady totally devoted to her husband and children. She died March 4,1923, after a lingering illness and was buried in the St. James Episcopal Cemetery. Her six sons served as her pallbearers just as they were to do two years later, almost to the day, when their father died on March 1, 1925, and was buried beside his wife.