"Kate and I have been looking for something to do together for 20 years, since our collaboration on Titanic, which was one of the most rewarding of my career," Cameron said in a statement.
"I can't wait to see her bring the character of Ronal to life," he continued.
Cameron is planning on releasing four sequels to 2009's Avatar starting with Avatar 2 arriving on Dec. 18, 2020 followed by Avatar 3 on Dec. 17, 2021. The series will then be taking a three-year break before returning with Avatar 4 on Dec. 20, 2024 and then Avatar 5 on Dec. 19, 2025.
Winslet joins a cast that includes returning stars Zoe Saldana, Sam Worthington, Sigourney Weaver and Stephen Lang whom Cameron has said will continue to be the main villain throughout the series. Fear the Walking Dead star Cliff Curtis is also set to be featured in a lead role.
Cameron began filming the first of the four sequels last week in California, Variety reported.