As early as 1912 Watkin accepted independent architectural commissions. Watkin's work falls into several categories: institutional (schools, social clubs, churches), commercial, and residential.
In 1912, Watkin was accepting independent architectural commissions. Between 1913 and 1915 he entered into partnership with George Endress of Austin, practicing under the name Endress and Watkin. This firm was dissolved at the end of 1919 and Watkin thereafter practiced under his own name. Watkin's association with Rice brought commissions from other educational institutions in Texas: Sam Houston Normal Institute in Huntsville, Sul Ross Normal Institute in Alpine, Texas A&M College in College Station, Victoria Junior College in Victoria, and the College of Industrial Arts (now Texas Women's University) in Denton. In 1924, in association with Sanguinet, Statts & Hedrick of Fort Worth, Watkin obtained the commission to develop a campus plan for the Texas Technological College in Lubbock, and to design the initial buildings - the Administration Building, the Textile Engineering Building, the Women's Building and the President's House. Watkin also served as consultant to the Houston School Board from 1924-1926, in connection with the design and construction of seven secondary school buildings. He laid out the campus of Kinkaid School in 1924, designing the lower school (1925), the gymnasium (1937), and the upper school (1946).
Watkin designed several facilities for the Young Men's and Young Women's Chrisitian Associations - a YMCA building in Beaumont, the YWCA Activities building in Houston (in association with Birdsall P. Briscoe and Maurice J. Sullivan) and the YWCA building in Galveston. In 1922 Watkin was called upon to prepare plans for the Museum of Fine Arts, a project completed in two stages, 1924 and 1926, for which Cram and Ferguson acted as consultants. He also received a number of commissions for structures in Houston Parks, designing the Miller Memorial Outdoor Theater (1921), activities centers for Root Square (1937), Hennessey Park and Proctor Plaza (1938), and the Garden Center in Hermann Park (1938-1940).
Ecclesiastical commissions included the First Methodist Church of Wichita Falls (1926, in association with Hedrick and Gottlieb), the Edward Albert Palmer Memorial Chapel (1927), St. Mark's Church, Beaumont (1942, in association with Stone & Pitts), the chancel reconstruction and Golding Chapel at Christ Church (1938-1939, in association with Carl A. Mulvey), and the Central Church of Christ (1940-1941, 1945-1947). Following his work on the Houston Public Library, Watkin prepared a proposal for a municipal library in Corpus Christi (1927) and served as consultant to Staub & Rather in the design of the Lake Charles, Louisiana, Public Library. From 1946-1951, Watkin, in association with Stayton Nunn, Milton McGinty, and Vance Phenix, was involved in the design and construction of the Methodist Hospital and Wiess Memorial Chapel.
Cram, Goodhue and Ferguson received work in Texas with which Watkin was associated as local representative as well. These projects included a parish house for St. Mark's, Beaumont (1915), Trinity Church (1917 - 1919), and the Autry House (1921). Watkin also represented the firm in the design of the Houston Public Library (1926) and a proposed South End Christian Church (1930).