Born in Brunswick, Coombs was the son of Hannah (Morse) and John Coombs, a shipbuilder. At the age of 17, George M. Coombs moved up the Androscoggin River to Lewiston, then a booming mill town, and worked as a carpenter until 1872.
That year, Coombs began working for Lewiston architect Charles F. Douglas. He remained with Douglas until his departure for Philadelphia in 1874. That year, he formed a partnership with Charles H. Kimball, a young architect from Portland. Due to economic instability, the two dissolved their partnership later that year, and Kimball returned to Portland. Coombs practiced alone until mid-1875, when he became the partner of William H. Stevens, another Lewiston architect. The firm of Stevens & Coombs lasted until Stevens' death in 1880. Coombs worked alone until 1896, when he established Coombs, Gibbs & Wilkinson with Eugene J. Gibbs and Harry C. Wilkinson. Wilkinson left in 1900, and Coombs and Gibbs worked together until Coombs' 1909 death. Upon his death he bequeathed his share in the firm to his son, Harry S. Coombs, who had worked for the firm since 1901. With him, Coombs & Gibbs survived until 1910.
Coombs became successful designing residences and institutional buildings throughout Lewiston, its twin city Auburn, and across the state, working in the prevailing Second Empire, Romanesque Revival and Queen Anne styles. The company is now Harriman Associates.
He married Clara Coffin and they had two sons. Both of them, Harry S. and Frederick N., worked for their father's firm.
Many of his works have been listed on the National Register of Historic Places.
Kimball & Coombs, 1874:
Albert F. Ames House, 73 Talbot Ave., Rockland, ME (1874)
Private practice, 1874-1875:
George C. Chase House, 16 Frye St., Lewiston, ME (1874)
Stevens & Coombs, 1875-1880:
William Bradford House, 54 Pine St., Lewiston, ME (1876) - Demolished 2007.
Farwell Bleachery, 39 S. Canal St., Lawrence, MA (1876–77) - Burned 1994.
Odd Fellows Block, 182–190 Lisbon St., Lewiston, ME (1876)
Edward Little High School, 30 Academy St., Auburn, ME (1877–78) - Demolished.
Charles Gay House, 64 Highland Ave., Auburn, ME (1878)
Lewiston Water Works, 38 Island Ave., Lewiston, ME (1878) - Only the gatehouse remains.
Auburn Engine House, 158 Court St., Auburn, ME (1879)
Chapel, S. Shore Ave., Squirrel Island, ME (1879–80)
Private practice, 1880-1896:
Dominican Block, 143 Lincoln St., Lewiston, ME (1882)
Music Hall Block, 200 Broadway, Farmington, ME (1882–83)
Louis J. Martel House, 122 Bartlett St. Lewiston, MA (1883)
Lothrop L. Blake House, 364 Main St., Lewiston, ME (1885)
Franklin County Courthouse, 140 Main St., Farmington, ME (1885)
First Congregational Church, 235 Main St., Farmington, ME (1887–88)
Savings Bank Block, 214 Broadway, Farmington, ME (1887)
Joseph H. Manley Cottage, 32 Club Rd., Small Point, ME (1888)
Charles L. Cushman House, 8 Cushman Pl., Auburn, ME (1889)
Harlow and Sanborn Pavilions, Maine Insane Hospital, Augusta, ME (1889–90) - Sanborn demolished.
Oak Street School, 36 Oak St., Lewiston, ME (1890)
Albert M. Penley House, 233 Main St., Auburn, ME (1890)
Cole Block, 19 Main St., Bethel, ME (1891)
Callahan Building, 276 Lisbon St. Lewiston ME (1892)
Walter Dingley House, 46 Elm St., Auburn, ME (1892)
Bradford Peck House, 506 Main St., Lewiston, ME (1893)
Norway Savings Bank Block, 300-306 Main St., Norway, ME (1894)
L. Linn Small House, 11 Elm St., Auburn, ME (1894)
Holman Day House, 2 Goff St., Auburn, ME (1895)
Oxford County Courthouse, 26 Western Ave., South Paris, ME (1895)
Coombs, Gibbs & Wilkinson, 1896-1900:
Peck's Dept. Store, 184 Main St., Lewiston, ME (1896)
James A. Walsh House, 253 Pine St., Lewiston, ME (1896)
Joseph Holman House, 227 Main St., Farmington, ME (1897)
Merrill Hall, Farmington State Normal School, Farmington ME (1897–98)
Lewiston Trust and Safe Deposit Building, 46 Lisbon St., Lewiston, ME (1898)
Bank Building, 38 Main St., Livermore Falls, ME (1899-1900)
Coombs & Gibbs, 1900-1910:
John D. Clifford House, 460 Main St., Lewiston, ME (1900)
Mt. Kineo House (Remodeling) and Cottages, Northwest Piscataquis, ME (1900) - Hotel demolished.
Masonic (Gateway) Building, 11 Lisbon St., Lewiston, ME (1901–02)
George Bonnallie House, 485 Main St., Lewiston, ME (1902)
Lewiston Public Library, Park & Pine Sts. Lewiston, ME (1902)
First National Bank Building, 157 Main St., Lewiston, ME (1903)
Fort Fairfield High School, Main & School Sts., Fort Fairfield, ME (1903) - Demolished.
Maine Trust and Banking Co. Building, 192 Water St., Gardiner, ME (1903) - Altered.
First National Bank Building, 18 Market Sq., Houlton, ME (1907)
Kennebec County Courthouse Annex, 95 State St., Augusta, ME (1907)
Philo Reed House, Main St., Fort Fairfield, ME (1907)
Wallace H. White House, 449 Main St., Lewiston, ME (1907)
Kora Temple, 11 Sabattus St., Lewiston, ME (1908–10)
Clifford Building, 217 Main St., Lewiston, ME (1909)
Gray and Staples Halls, Maine School for the Feeble-Minded, New Gloucester, ME (1909)
Norway Grange No. 45, 15 Whitman St., Norway, ME (1909)
Callahan Block, 282 Lisbon St., Lewiston, ME (1910)
Main Building, Central Maine General Hospital, Lewiston, ME (1910)
