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.
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.