The shows will be their first concerts since breaking up in 2001, and the first with all five of the original group since Geri "Ginger Spice" Halliwell quit to pursue a solo career in 1998.
"Imagine you got divorced and you've got back together with your ex-husband," Halliwell said, explaining how she felt about the reunion.
"She just appreciates the fact we've let her back in," joked Victoria "Posh Spice" Beckham.
The group said the shows would be in Los Angeles on Dec. 7; Las Vegas on Dec. 8; New York on Dec. 11; London on Dec. 15; Cologne, Germany, on Dec. 20; Madrid, Spain, on Dec. 23; Beijing on Jan. 10; Hong Kong on Jan. 12; Sydney, Australia, on Jan. 17; Cape Town, South Africa, on Jan. 20; and Buenos Aires, Argentina on Jan. 24.
Halliwell and Beckham joined with Melanie "Sporty Spice" Chisholm, Emma "Baby Spice" Bunton and Melanie "Scary Spice" Brown to pose for photos and announce tour plans.
"We wanted to say thank you to our fans. It just feels very right for us," Chisholm said.
"Obviously it's nostalgic. But equally, if new fans want to come along, that's fantastic," Halliwell said. "I like to think our songs are universal and they are timeless."
Fans stood outside the news conference, hoping to catch a glimpse of the Spice Girls.
"We found out about this going on and we decided to take a trip," said Nicola Seodon, 21, a shop worker, who traveled the 20 miles from Dartford to London.
"I was a big Spice Girls fan when I was 10 years old. I'll definitely buy their album and I never got to see a concert when they were still around, so this will be a great chance," she said.
The Spice Girls' first single, "Wannabe," was released in 1996 and topped charts in 31 countries. They went on to sell more than 55 million records.
But their last album, "Forever," released in 2000 and without Halliwell, fared poorly.
You could now call them the Spice Mums. Beckham said the tour would be designed to accommodate the band members' seven children. And Bunton is now pregnant with her first child.
"Our priority is going to be our families. We want to have fun," said Beckham, who has three sons with her husband, soccer star David Beckham. "That's one of the many reasons for this, for our children to see what we used to do. And I may be the cool one in the family for once."
EMI said it plans to release the first Spice Girls greatest-hits album in November. The group also plans to make their first official documentary for TV broadcast.
"It's going to be the most honest story that you've ever heard," Halliwell said. "You get to see the dark side of the Spice Girls, the gritty side, the tears."