Griffith purchased and drained the bogland at Pollagh, part of the Bog of Allen, a peat fuelled power station was built which drove an excavator, excess peat being taken by the Grand Canal for sale in Dublin. The site was sold to the Turf Development Board in 1936 who used it as a basis for all of their later peat fuelled power stations, the area is now a nature reserve.
Griffith received a knighthood in 1911 and became vice-president of Royal Dublin Society in 1922. He served as Honorary Professor of Harbour Engineering in Trinity College, his alma mater, and received an honorary M.A.I. degree from the University of Dublin in 1914. From 1922 he was an elected member of the Seanad Éireann, the Irish senate, until its abolition in 1936. In the 1930s he and his wife, Sarah Purser, endowed the Purser Griffith Travelling Scholarship and the Purser Griffith Prize to the two best performing students in European Art History at University College Dublin.
He died at Rathmines Castle in Dublin on 21 October 1938.