He worked almost exclusively for Sir Watkin Williams Wynn of Wynnstay, Ruabon and the Grosvenor family of Eaton Hall near Chester.

[1] Gummow is first noted as a clerk of the works for the architect Samuel Pepys Cockerell for the alterations to St Margaret's Church, Westminster from 1799 to 1802.

from Lord Grosvenor and Sir W.W. and is not allowed any other charge or profits – but has his lodgings and livings – out of this he has saved an easy independence".

Sir Howard Colvin summed up Gummow's work as follows "Though not an architect of the first rank, his additions to Eaton Hall successfully maintained the elegant rococo Gothic of the main block designed by Porden and at Brogontyn his Ionic portico is a handsome addition to an existing classical house".

Benjamin and Michael Gummow appear to have worked together on the rebuilding of Cleveland House St. James, Westminster around 1800.