Sweden defender Helander has signed a four-year deal in Glasgow pending international clearance.
Rangers reportedly paid £3.5 million ($6.3 million) to prise him from Bologna.
The towering centre-back made 20 appearances in Serie A last season and arrives at Ibrox with 10 caps of international experience.
"I am delighted to be joining Rangers, it's a special club with tremendous fans and a unique history," Helander said after the move was announced on Sunday (AEST).
"The opportunity to work with a manager like Steven Gerrard was an easy decision to make.
"I've come here to battle for every point and to win trophies and I'm looking forward to meeting my team-mates and getting started."
Rangers finished second in the Scottish Professional Football League last season, Gerrard's first in charge.