He was born in St. Peter on 20 November 1820 and studied at the University of Caen and the Sorbonne. He was admitted to the Bar of Jersey as advocate in 1845, but in 1846 the family moved to Blois in France as a result of his mother's ill health. Returning to Jersey, he entered the political scene and was elected Constable of St. Helier in 1856. During his short term in municipal office, he laid out the Parade as an urban promenade.
The death of the Bailiff, Sir Thomas Le Breton, created a vacancy among the Crown Officers and on 6 March 1858 Robert Pipon Marett was appointed Solicitor-General. He rose through the legal hierarchy, becoming Attorney-General in 1866, and Bailiff in 1880.
He died on the 10 November 1884 at his home, La Haule Manor in St. Brelade, after a long illness.
His La Fille Malade was widely admired and François-Victor Hugo reproduced it in his La Normandie inconnue. It has been suggested  that his Lé R'tou du Terre-Neuvi oprès san prumi viage influenced Victor Hugo's Les Pauvres gens written in Jersey in 1854. He corresponded publicly in verse form with George Métivier, the Guernsey poet. His comparatively small poetic output belies its continuing influence. His poetry is generally social rather than political, but La Bouonne Femme et ses Cotillons satirises conservative resistance to constitutional reform.
He took a philological interest in Jèrriais and through his prestige did much to standardise Jèrriais orthography on the pattern of French orthography. On being appointed to high office he stopped publishing poetry, and a fire at his home, Blanc Pignon, in St. Brelade in 1874 destroyed his papers - a loss to Jèrriais literature.