Although G. W. Hewitt was born in Philadelphia, his parents, George Washington and Annie B. Hewitt, soon moved to Burlington, NJ, where young Hewitt attended Burlington College before returning to Philadelphia to enter the architectural office of Joseph C. Hoxie in 1857. By 1857 Hoxie's brief partnership with Stephen D. Button had been dissolved, and he was adjusting to the economic panic of 1857. Hewitt, however, remained with Hoxie until 1859, weathering the economic setbacks of the time and gaining office training in the ecclesiastic projects at which Hoxie excelled. Following his training in Hoxie's office, Hewitt transferred to the office of John Notman, with whom he associated from 1859 until Notman's death in 1865. During Hewitt's tenure with Notman, St. Clements church and Parish school (20th and Cherry streets, Philadelphia) and Holy Trinity Church (19th and Walnut streets) were being completed, and Hewitt would again gain from an older architect a thorough grounding in appropriate church style. Many of Notman's church designs of this time were in the English Gothic Revival so popular following the construction of Philadelphia's St. James the Less, and later Hewitt would call upon his background in this style for St. Martin-in-the-Fields Church, designed with is brother William D. Hewitt.

After Notman's death, Hewitt entered John Fraser's office where he was instrumental in the construction of the tower for St. Marks Church, which had been left unfinished at the time of Notman's death. While in the employ of Fraser, Hewitt became acquainted with Frank Furness, and in 1867 the new firm of Fraser, Furness & Hewitt was established. This office would become Furness & Hewitt in 1871 when Fraser resigned and moved to Washington, DC, as Acting Supervising Architect of the Treasury Department.

During Hewitt's collaboration with Furness, he maintained his interest in ecclesiastical projects, supervising the design of the Church of the Holy Apostles, 21st and Christian streets, Philadelphia (1868-70), The Lutheran Church of the Holy Communion, Broad and Arch streets, Philadelphia (1870-75; demolished), St. James Episcopal Church, 22nd and Walnut streets (1870-71; demolished), and St. Peters Episcopal Church, 6000 Wayne Avenue, Philadelphia (1873). In 1875 Furness & Hewitt dissolved their partnership by mutual agreement, and Hewitt practiced on his own from 1875 to 1878 when he added the name of his younger brother William D. Hewitt to the office. This association with his brother, under the name G. W. & W. D. Hewitt continued until George Hewitt retired in 1907. During his retirement Hewitt continued his two favorite hobbies: astronomy and photography. His home in Burlington, NJ, included a well-equipped private observatory.

Hewitt was also a member of the board of the Mercantile Library, Philadelphia, and president of the Burlington (NJ) Library.

Written by Sandra L. Tatman.