Booth worked as director of rugby with London Irish before spells as first-team coach with Bath and assistant coach at Quins before joining Ospreys, who he guided to the URC play-offs in the 2023-24 season.
Australian Gilmore, a former assistant and interim head coach at the Waratahs, joined Quins as defence coach prior to last season.
“Jason has made a positive impact within the performance group since his arrival at the club and will assume this leadership role within what is an already established and experienced coaching group,” chief executive Laurie Dalrymple told the club’s website, external.
“Similarly, we’re equally pleased to welcome back Toby as a forwards consultant, who has a strong understanding of our club and playing identity.
“As the season progresses, we will continue to review our coaching structure for the long term but for now, our full focus is this week’s fixture against Leicester Tigers in the Prem Cup and next Friday’s Gallagher Prem opener against Bath Rugby at a sold-out Stoop.”
