 From 1819 Mylne was engaged in laying out residential streets on the New River Company's property at Clerkenwell, including Myddelton Square, Amwell Street, Inglebert Street, and River Street.Mylne later designed the gothic St Mark's Church, Myddelton Square (1826–1828), and Clerkenwell Parochial Charity Schools (1828).Mylne designed several bridges, including the iron Garret Hostel Bridge in Cambridge (1835–1837, demolished 1960), and repairs to the Caversham Bridge in Reading (1815).