Part of an economic development programme from not-for-profit agency Sea Change Sussex, the new conference centre uses a biomass boiler for heating, has a shingle roof for wild plants and insects and collects rainwater for use in its sewer system.
Sussex Exchange has three rooms for meetings and events, with the largest – the Forest Room – accommodating up to 130 delegates theatre-style or 96 in cabaret layout.
The Meadow Room can accommodate up to 22 in boardroom format or 35 people theatre-style.
Sussex Exchange also has a 52-seat cinema for presentations and lectures and a restaurant with balcony.
Sea Space regeneration company funded the main building works with £2.3m investment, while Sea Change paid for the £200,000 internal work.
The centre is planned to open in September.