Robert Swain Peabody (1845 – September 23, 1917) was a prominent Boston architect.
Peabody was born in New Bedford, Massachusetts, and was the cofounder of the firm Peabody & Stearns. He was an early supporter of the Colonial Revival style and had an affection for English styles and the Picturesque Movement and Beaux-Arts architecture. He attended Harvard University in Cambridge, Massachusetts and the École nationale supérieure des Beaux-Arts in Paris. He was elected an Associate of the American Institute of Architects in 1874 and a Fellow in 1889. He was president of the Institute from 1900 to 1901. He was also a member of the Society of Beaux-Arts Architects and the Boston Architectural Club. He was chairman of the Boston Park Commission. He married Annie P. Putnam in 1871, and the couple had three children: Ellen (1872), Arthur John Peabody (1875) and Catherine Putnam (1877). He died, aged 72, in Marblehead, Massachusetts.