He became grand sachem after sachem Tatobem was killed in 1632. Under the sachemUncas, the Mohegan rebelled against domination by the Pequot. Sassacus and the Pequot were defeated by the English along with their Narragansett and Mohegan allies in the Pequot War.
Sassacus fled to what he thought was safety among the IroquoisMohawk in present-day New York, but they murdered him. They sent his scalp to the English as a symbolic offering of friendship with the Connecticut Colony.