The Addicks, currently third in npower League One, have been searching for new investment since they were relegated from the Barclays Premier League in 2007.
Lawyer and businessman Slater becomes the club's new chairman and Jimenez, who briefly held the post of vice-president (player recruitment) at Newcastle, will be on the board along with outgoing chairman Richard Murray and former chief executive Peter Varney.
"We are delighted to have taken control of Charlton," Slater, 44, told the club's official website. "The club has a long and proud history and has an incredibly loyal fanbase.
"I'd like to pay tribute to Richard Murray, who took on a huge financial responsibility last summer when he saved the club from almost certain administration while he sought new investment.
"The acquisition brings much-needed financial stability to the club. Our plan is to run the club on a sensible financial footing and develop a commercial plan to ensure we make progress on and off the pitch to meet the expectation of the fans. What we won't do is create unrealistic pie-in-the-sky expectations."