Baker was trained to paint miniatures by his father. Within the first year after commencing his professional career at the age of sixteen, he had executed over 140 miniatures. He began exhibiting his miniatures in the National Academy of Design's annual exhibitions in 1838. In 1841 enrolled in its school, passing that and the following school year studying in the antique class, perhaps in a move to enlarge the scale and range of his capabilities. In 1844 he traveled to Europe where he spent considerable time in Italy studying the works of the old masters.
Upon returning in 1846, Baker restablished himself in New York, and soon proved as facile in full scale portraiture as he had in miniature painting. Although he frequently executed genre paintings, his reputation as a portraitist continued to grow throughout the mid-nineteenth century; frequently he had a waiting list of sitters. Around 1866 Baker purchased a residence in Darien, Connecticut, but maintained a studio in New York throughout his career.
Baker was notably active in Academy affairs: he was repeatedly elected to the Council, serving 1852-54, 1859-61, 1862-66, and finally a one-year term 1868-69; from 1863 to 1864 he was on the Fellowship Fund Committee, which pursued financial donations to sustain the Academy's operations; and from 1867 to 1869 he was a visitor to the Academy's school. His portraits were exhibited consisently in Academy annual exhibitions up to the year before his death.
Baker's sustained success as a portraitist was explained in The Art Journal:
The late Mr. George A. Baker, of the National Academy of Design, was one of the most popular portrait painters of his time. He never took rank with [Charles Loring] Elliott or [William] Page, and probably did not claim such fellowship, but he was perhaps at the head of that group who pleased sitters not by artistic arrangement of drapery and other factitious devices but by "keying up," so to speak, whatever attractiveness the face and character to be painted might originally possess.
