The Croatians, gold medalists in 1996 and 2004, beat Iceland 31-28 on home soil in Varazdin on Sunday as both teams advanced from that group following easy wins over Japan and Chile.
They were joined by treble Olympic silver medallists Sweden, Hungary, Serbia and Spain.
World champions France, European title holders Denmark, Argentina, Tunisia and South Korea had already booked their Olympic berths alongside hosts Britain.
Having finished third in January's European Championship in Serbia, the Croatians will now head to the Olympics eager to add more silverware to their trophy cabinet which already includes the 2003 world title and five other silver medals from major events.
"We are as hungry as ever to get results and we will go to London with the ambition to win another medal but we can't promise one because it will be a very strong field," Croatia coach Slavko Goluza told the Balkan country's media.
"We now have enough time to improve and hit top form for the Olympics because I saw some chinks in our armour too," said Goluza, who was a key player in both Croatian outfits that won Olympic gold medals.
Their neighbours and traditional rivals Serbia qualified for the first time as an independent nation after a 26-18 win over Algeria coupled with Spain's 33-22 rout of Poland in Alicante which also sent the 2005 world champions through.
Euro 2012 runners-up Serbia won their first medal as a single nation on home soil in January and coach Veselin Vukovic was confident they could spring another upset in London.
"The important thing is that we have traced the path to a consistent run because having won the European Championship silver medal, we will now take part in the Olympics and next year's world championship in Spain," Vukovic said.
"Fans should not expect us to win a medal in each major event we reach although miracles do happen with a bit of luck," added Vukovic, who won the 1984 Olympic gold medal as a player with the former Yugoslavia.
Sweden, who have won four world and as many European titles but are yet to be crowned Olympic champions, cruised through their qualifying group in Gothenburg with comfortable wins over Hungary, Brazil and Macedonia.
The Hungarians, craving an Olympic medal after finishing fourth four times, clinched the last remaining berth with tight wins against Brazil and Macedonia before going down 26-23 to the Swedes.