The 23-year-old is available for selection immediately having agreed a two-and-a-half-year deal with Richard Cockerill’s side.
Van der Walt came up through the ranks at Golden Lions, playing for the Ellis Park side at every age-grade.
His first team debut came in the 2014 season and he scored 147 points in 33 appearances for the Johannesburg team.
Van der Walt’s Super Rugby debut for the Emirates Lions came in 2015, and the fly-half made 22 appearances as Swys de Bruin’s side reached the Super Rugby final this year.
Edinburgh head coach Richard Cockerill said: “Jaco is a skilful young player who is equally adept at stand-off or fullback.
“He’s an excellent goal kicker and will provide cover in key areas for us.
“We’re delighted that he’s chosen to be part of what we’re building here at Edinburgh.”