During his time at Belvedere he was responsible for the alteration of the Diocletian windows on the upper façade and for the addition of the terracing.

He commissioned Ninian Niven, curator of the Botanic Gardens in Glasnevin to draw up plans for the Victorian Walled Garden.

James Woods author of “The Annals of Westmeath” describes Marlay as one of the best landlords in Westmeath.