The news comes after shareholders in Spirit Nextel, the third biggest wireless operator in the US, backed the company’s revised bid for a 78 percent stake in the business.
In taking control of this stake SoftBank will pay $21.6 billion, a figure that makes it the largest overseas acquisition by a Japanese firm in history.
"The transaction with SoftBank should enhance Sprint's long-term value and competitive position by creating a company with greater financial flexibility," Dan Hesse, chief executive of Sprint said in a statement.