He completed a classical education by the age of 16, then trained with Sir Thomas Hine at a builder in Nottingham, and then took on an apprenticeship with an architectural firm in London.

Barnett left England for the United States in early 1839, remaining in New York City for six months before departing for St.

[1] His works included houses, churches, commercial, and civic structures.

Among his best known structures are renovations to the Old Courthouse, the Missouri Governor's mansion, the structures of the Missouri Botanical Garden, Tower Grove Park, and the Southern Hotel.

[4] His eldest son, Absalom J. Barnett, became a successful architect in San Francisco.