, whose character of Grace Augustine died in Avatar, is returning in the James Cameron
-directed sequels in a different role.
Cameron is all set to direct three more Avatar movies and he begins production on the new film later this year.
Weaver will join previously announced cast returnees Sam Worthington, Zoe Saldana and Stephen Lang, said the Hollywood Reporter.
"Sigourney and I have a long creative history, dating back to 1985 when we made Aliens. We're good friends who've always worked well together, so it just feels right that she's coming back for the Avatar sequels," Cameron said in a statement.
"Her character of Grace Augustine, as fans know, died in the first movie, so she's playing a different and in many ways more challenging character in the upcoming films. We're both looking forward to this new creative challenge, the latest chapter in our long and continuing collaboration," he added.
Read: Avatar fan? Cameron has three more films lined up for you
The as-yet-untitled Avatar sequels will be filmed back-to-back. The first will be released in December 2016, with the second to follow in December 2017 and the third a year later. The movies will be produced by Cameron and Jon Landau via their Lightstorm Entertainment.
Released in December 2009, Avatar is the top-grossing film of all time at the worldwide box office, earning USD 2.8 billion.