Most of the agreement's details between the The Metlakatla (MET'-la-CAT'-la) Governing Council and the Petronas-led company are being kept confidential.
However, a statement says the deal covers the nation's environmental concerns and comes after "intensive negotiation" between the two parties and the province.
Under the agreement, the Metlakatla is being paid for signing on and for providing a letter of support around the project.
Chief Harold Leighton says his nation has weighed the pros and cons of the proposed terminal at Lelu Island and feels this is the best deal possible.
Earlier this month, Petronas said it was delaying its LNG terminal in northwestern B.C., because conditions weren't right to proceed with it's $36-billion project.
The Nisga'a Nation recently signed a separate agreement around the proposed LNG terminal that includes removing more than 63 hectares of land from the Nisga'a Memorial Lava Bed Park.
Note to readers: CORRECTS fixes typo