Before he came to Sheffield, Marnock worked as the head gardener in Bretton Hall (now the Yorkshire Sculpture Park), Wakefield between 1829 and 1833.

He left this post in 1863 but continued to practise in his profession as a landscape gardener until 1879, during this time he returned to Sheffield for two commissions, Thornbury in 1865 and Weston Park in 1873.

[1] Another of his achievements was the landscaping in the 1870s of the grounds of Avenue House, Finchley, north London, the property of ink magnate and local MP Henry Charles Stephens.

Since then, the estate has benefited from National Lottery money to restore Marnock's designs to their original grandeur.

[2] One of the best preserved examples of his work is Dunorlan Park in Royal Tunbridge Wells which has recently undergone a £2.8 million transformation[3] to restore it to the original Marnock design.