Iceland, the lowest ranked of the eight teams at No. 46 in the world, will host the first leg against Croatia, which fired its coach last week.
The four winners will complete Europe's 13 entries in the 32-team World Cup.
Ronaldo and Ibrahimovic were consigned to the playoffs after their teams finished second in their qualifying groups.
Portugal also had to advance to the 2010 World Cup through a playoff after twice tying 0-0 with Sweden in the group.
France, the 2006 World Cup runner-up, also makes its second straight trip to the playoffs. Four years ago, a handball by Thierry Henry helped France beat Ireland in extra time.
Iceland, which has a population of about 315,000, aims to become the smallest country ever to play at the World Cup. That record is held by 2006 qualifier Trinidad and Tobago, which had about 1.2 million.
Iceland coach Lars Lagerback is aiming for his fourth straight World Cup with three different teams. He coached his native Sweden at the 2002 and 2006 tournaments and Nigeria in 2010.
Croatia's playoff matches will mark the coaching debut of Niko Kovac. The 42-year-old Kovac stepped up from coaching the under-21 team to replace Igor Stimac, who was fired after a series of poor results.