The two-year contract from DUR Hospitality has an estimated value to Hill of approximately US$2.7m (£1.9m).
The five-star hotel will have 80 hotel rooms and 140 residential apartments. It will include a conference centre, ballroom and a 220-space car park. The 39,000m2 project is expected to achieve LEED Silver certification.
"We are very excited to help deliver the Diplomatic Quarter Marriott Hotel for DUR," said Mohammed Al Rais, regional president (Middle East) for Hill's project management group. "The project will be an asset to Riyadh's hospitality and tourism sector."