Surrey-based Gavin Jones undertook landscaping works at the university's Whitelands College site last year and has since been maintaining the campus.
Staff will now begin work on the rest of the 22ha grounds, based near Putney, south-west London.
Gavin Jones business development manager Yvette Etcell said the contract would provide a wide range of work. "This is a great win for Gavin Jones and is testament to the quality of the landscaping works and grounds maintenance already undertaken by our teams at Whitelands College," she said.
"Roehampton is somewhat unique, offering a diverse range of building styles and a varied landscape; from traditional gardens at Froebel College to the more modern, minimalistic style at Southlands College.
"This diversity of style presents us with a perfect opportunity to showcase our range of horticultural skills, and we are delighted to have been successful in adding it to our growing portfolio of university, college and school contracts for grounds maintenance."