Mitchells & Butlers (M&B) has acquired a minority stake in 3Sixty Restaurants from serial restaurant investor Luke Johnson.
As a result, M&B have entered a formal partnership to accelerate the expansion of 3Sixty's Ego brand.
Johnson has now stepped down as chairman and director of 3Sixty. Fellow directors Michael Gottlieb and Joseph Tager have also resigned.
The Mediterranean-inspired Ego brand already leases and operates three of the M&B sites as part of its 17-strong portfolio: the Hollybush in Stockton Brook, Stoke; Tumbledown Farm in Cannock; and the Fox Cub near Preston.
James Horler, chief executive of 3Sixty, said: "We already enjoy a successful trading relationship with Mitchells & Butlers, so the establishment of this joint venture feels like a logical progression, leaving us well placed to grow the Ego brand in future."
Chris Hopkins, commercial and marketing director of Mitchells & Butlers said: "We're delighted to formalise our partnership with the Ego team. Working together presents us with a great opportunity to learn from each other's businesses and experiences to the mutual benefit of both companies."
Earlier in the month 3Sixty Restaurants announced a reduction in its pre-tax losses after selling three Rocket restaurants last year to focus on expanding Ego.
The company posted sales of £19.5m in the 12 months to 25 March 2018 to Companies House. The figure marks an increase on the £18.8m turnover seen in the previous year.