Flintshire County Council has appointed the firm for the project to upgrade the 1970s-built complex with work set to start this year.
The 45-year-old theatre will be extensively refurbished and repaired, along with significant improvements to deliver a more energy-efficient building.
This will bring large savings on gas, electricity, and water costs, and make better use of resources.
The thermal envelope of the building will be improved, and renewable energy sources including PV panels and air source heat pumps installed to improve energy consumption. All services and theatre equipment will be replaced throughout the building.
A new timber extension at the front of the building will provide a new, welcoming foyer space at three floors and contains a new double height restaurant, bar and café, as well as a meeting room and Green Room.
Two new rehearsal rooms will be constructed, including a full-height room that can take a rehearsal for the Anthony Hopkins Theatre stage, the Clwyd Room will be refurbished with the floor raised to all one level.