Sendejo agreed to a four-year contract, a person with knowledge of the deal told The Associated Press. The person spoke on condition of anonymity because the move had not been officially announced.
Sendejo could have tested the free-agent waters beginning on Wednesday, but instead elected to return for a sixth season in purple.
The Vikings gave Sendejo a contract extension in 2013, largely for his special-teams work at that point, but he turned himself into a serviceable NFL safety who enjoyed his best season in 2015.
Coach Mike Zimmer said at the NFL combine that the Vikings were looking for another playmaker to allow Smith some more freedom and acknowledged he wasn't sure if that player was on the roster. It's not immediately clear if Sendejo's deal, which was first reported by Fox Sports, will keep the Vikings from looking for another safety or if they plan to give the job to Sendejo.
Ellis got a one-year deal, agent Drew Smith said. Ellis joined the Vikings last October after being let go by the New York Giants and played in nine games for Minnesota. He was a third-round draft pick by the New York Jets in 2011.
ESPN Vikings reporter Ben Goessling contributed to this report.