Manningham died 26 August, 1809 in Maidstone from illness contracted during the Retreat to Corunna in the opening stage of the Peninsular War in which the 95th Rifles were to demonstrate the tactical value of the approach developed by Manningham and Stewart. He is buried in the churchyard of All Saints in Little Bookham but a memorial is also placed in the west aisle of the north transept in Westminster Abbey.