Collcutt was apprenticed to the London architect R. E. Armstrong, and then employed by the partnership Miles and Murgatroyd. He began working in the establishment of George Edmund Street, with Richard Norman Shaw, before setting up his own practice in 1873 and achieving recognition, winning the Wakefield Town Hall competition in 1877, the Grand Prix for Architecture at the Paris International Exposition in 1889, and the Royal Gold Medal in 1902. He was a Fellow of the Royal Institute of British Architects, and served as its president from 1906 to 1908. He was a member of the Société Centrale d’Architecture de Belgique, and the Société des Artistes Français.