Wallace married the former Susan E. Lyon in 1831. He became a partner in a Knoxville, Tennessee mercantile in 1834. later assumed the presidency of the East Tennessee & Georgia Railroad in 1853 and held that position until the Civil War. Afterward he planned to become a farmer, but Georgia Governor Charles Jenkins appointed him as superintendent of the Western & Alabama Railroad from 1866 to 1868. In 1869 he contracted with Samuel Tate to complete the unfinished South & North Alabama Railroad from Montgomery to Decatur.
Meanwhile, Wallace was president of the Atlanta State National Bank (later the Merchants' Bank). In 1879 he was appointed to the Georgia Railroad Commission and was made chairman in 1883. He was also an elder in the Presbyterian church for many years. He died in Atlanta in 1895.