Robert was the younger of two boys born to Vice-Admiral Horace Walker Longden C.M.G and his wife, Emily Gretchen Hewitt. His Longden grandfather, Sir James Longden, had been Governor of Ceylon and British Guinea where Horace was born.

Robert was born in 1904, at Lisle Court, Wootton on the Isle of Wight, the home of his maternal grandmother, Ernestine Hewitt nee Paton.

His grandfather, Alfred Hewitt had bought the house on 9 July 1891 for £3500. He had been a sugar planter at Playstowe Plantation, Mackay, Queensland, Australia and was living temporarily at 28 Park Crescent, Middlesex. He died on 6 November 1897 leaving property in Australia and London valued at £6274. 0s. 10d to his wife.  She died at the age of 58 in October 1908. The house was left in Trust for their five surviving children, Augustine Ernestine, Alfred Scott, Emily Gretchen, Amee Gerda and Robert Paton Hewitt. The Trustees sold the house on 28 March 1919.

Robert was a Scholar of Trinity College and Fellow of Magdalen College before being appointed a Student of Christ Church in 1928. Earlier that year, he’d spent some time in North Africa and returned to England on 28 April from Algiers.

In 1931, his Notes on the Parthian Campaigns of Trajan were published in The Journal of Roman Studies Vol. 21. He assisted with the cataloguing of the Wilshere Collection at Pusey House.

He held the post of Censor at Christ Church when he was appointed Master of Wellington College, Berkshire in 1937. In the early summer, he holidayed in the United States with his parents, returning to Southampton on the Georgic on 19 July.

He was killed during a bombing raid whilst on Home Guard duties at Wellington on 8 October  1940.

His name is on the Memorials at Magdalen College, Wellington College and on the Crowthorne War Memorial.