NFL Network's Andrew Siciliano reports the five-year extension is worth $50 million, including $22 million guaranteed, according to a source with knowledge of the negotiations.
Flowers took to Twitter to thank his fans for congratulating him.
"wanted to be a chief forever and we made it happen," he wrote.
Flowers, a second-round pick of the Chiefs in 2008, was playing under his original rookie contract, according to The Star. The 25-year-old has been a mainstay in the starting lineup since he was drafted, starting 44 of his 45 career games for the Chiefs.