Sent by the firm to establish a branch office in St. Louis, his employers closed shop there in 1900 and Mauran formed his own partnership, Mauran, Russell & Garden, which evolved into Mauran, Russell & Crowell in 1911.
From 1902 Mauran became a Fellow of the American Institute of Architects, and was appointed by Theodore Roosevelt to the first United States Commission of Fine Arts in 1910.