Boyd, who has signed a one-year deal, scored 101 goals in 143 games during his time at Ibrox between 2006-2010.
The 30-year-old rejected approaches from a number of clubs - including SPFL rivals Aberdeen and Dundee United - to join the Championship side.
Last season Boyd, who has been capped 18 times by his country, helped Kilmarnock preserve their Premiership status with 25 goals in 43 appearances.
He will be joined at the head of Rangers' attack next season by 34-year-old Kenny Miller, who signed a one-year deal earlier this month after being released by Vancouver Whitecaps.
Speaking after his medical, the former Middlesbrough and Portland Timbers striker said: "I’m thrilled to be back, I’m a Rangers fan and I know everything about the club. I’m really looking forward to the new season and it will be a tough but exciting challenge.
“In football it’s strange because you never know what can happen but as soon as I knew there was a bit of interest in me from Rangers there was only one place I was going.”
Rangers manager Ally McCoist said: "We’re delighted to announce that Kris has signed a one-year deal with us this morning.
“We’ve been speaking to him for a few days now and he obviously showed a great desire to come back and we were very keen for him to come back. It’s great news for the club."
Since being consigned to liquidation in the summer of 2012 Rangers have eased to the title in the bottom two tiers of Scottish football but they will face a much sterner challenge next season.
Edinburgh duo Hibernian and Hearts, both relegated from the Premiership, are among the full-time opposition which stand in their way of a place in the top-flight.