The move comes after No. 3 running back Corey Grant was placed on injured reserve with a Lisfranc injury in his left foot. Grant had been pressed into playing time with regular starter Leonard Fournette out indefinitely because of a right hamstring injury and No. 2 back T.J. Yeldon playing with a nagging ankle injury.
The Jaguars also promoted first-year back Brandon Wilds from the practice squad, but he has been a non-factor with the ball and a liability as a blocker.
Charles, 31, who worked out for the Jaguars on Tuesday morning prior to signing the deal, said he'd been waiting for the right opportunity to sign with a contender.
"I've been trying to do all my condition work, just trying to stay in shape just in case I got anybody to call," Charles said Tuesday. "The reason why I wanted to come here, really, was because I wanted a potential shot at a Super Bowl. That's why I still kept my options open. I really want to win a championship."
He should be able to pick up the offense quickly and make an immediate contribution Sunday at Dallas (2-3) while playing behind Yeldon.
"I have a lot [left in the tank] and I've got to prove a lot," Charles said. "Opportunities don't come around like this all the time."
Charles spent nine years in Kansas City and played 14 games with the Denver Broncos last season. The four-time Pro Bowl selection has 7,556 yards rushing and 44 touchdowns, plus 2,586 yards receiving and 20 more scores.
"In my mind, I want to come here and make my own history," Charles said. "I want to start a new history. Everybody says, 'he's old' right now, but I want to start something new. ... I want to do something special for the Jaguars. I hope we can go all the way."
The 2017 season didn't work the way Charles or the Broncos had hoped. In May 2017, the Broncos signed Charles to a one-year deal after he was released by the Chiefs. However, by season's end, he was an afterthought in the offense.
Charles was a healthy game-day inactive for the Broncos' final two games and finished the season with 69 carries for 296 yards.
He publicly expressed his frustration late in the season when he said the Broncos should release him if he wasn't going to play more. At the time, coach Vance Joseph said simply "that had not been a thought for us."
Charles became the leading rusher in Chiefs history (7,260 yards) despite a series of knee injuries. He had four seasons with at least 40 receptions.
He tore his right ACL in October 2015 -- the second such tear of his career after tearing the left one in 2011 -- and had multiple knee surgeries in 2016. Charles was adamant throughout last season that he can be a regular contributor, despite his past knee troubles.
He has a career average of 5.4 yards per carry.
ESPN's Michael DiRocco, Jeff Legwold and The Associated Press contributed to this report.