The Chiefs did not disclose terms of the deal, but multiple media outlets reported it was a four-year, $68 million contract, with $45 million of it guaranteed.
"It was a priority of ours to get this deal done and keep Alex in a Chiefs uniform long-term," Chiefs general manager John Dorsey said in a statement released by the team. "Alex is a proven leader on and off the field. He is a special individual with a lot of ability, and we are fortunate to have him here."
In his first year with the Chiefs last season, Smith completed 60.6 percent of his passes with 23 touchdowns and seven interceptions while leading Kansas City to an 11-5 regular-season record and a playoff berth.
"John and his staff along with Tom (Condon, Smith's agent) and his group have worked hard to get this deal done. They've done a nice job," Chiefs head coach Andy Reid said in a statement. "Alex is a smart, talented football player that has adapted well to our offensive scheme. He also, obviously, has had a tremendous amount of success as a quarterback in this league. We as a team are very happy to have Alex as our quarterback moving forward."