They added his name as the last on their team of 125 track and field athletes.
Pistorius ran 45.07 seconds last year and opened this season with a 45.20 - both Olympic-qualifying times.
But he needed another 45.30 or better at an international meet before last Saturday to seal a spot in the 400, according to his national Olympic committee's regulations. Pistorius missed it by less than a quarter of a second in his final qualifying race at the African Championships.
"Today is truly one of the proudest days of my life," said the multiple Paralympic champion, who had both his legs amputated below the knee at 11 months old. With the selection, Pistorius realizes his dream of competing at an Olympics and Paralympics in the same year.
After he missed out on his second required Olympic qualifying time, the South African Olympic committee and Athletics South Africa appeared certain to overlook him in the 400. They had insisted throughout the season that they wouldn't relax their tough qualifying criteria for Pistorius.
But the late-season burst at the Africans, which also won him a silver and his first major individual medal in an able-bodied race, may have pushed officials to include him.
"Since he's going to be [in London], our decision is he can run both," Olympic committee chief executive Tubby Reddy told the Associated Press. "There's no reason why he can't. Our decision is he can."
Pistorius has always maintained a place in the 400 final at the Olympics was his ultimate career goal, even before he had to take his case to sport's highest court to be allowed to compete against able-bodied athletes on his blades. Some still argue they give him an unfair advantage, but he was cleared in 2008 and has never looked back.
Controversy could still follow Pistorius at the Olympics if there's opposition to his running on his blades in any leg of the relay other than the first. Fears over the safety of other athletes, when runners bunch in the inside lane for the later legs, have been raised.
France's Noah out. Chicago Bulls center Joakim Noah will not play for France at the London Olympics because of a left ankle injury.
"I'm absolutely not ready," Noah said in L'Equipe newspaper. "Not ready to run, not ready to jump. And even less to play."
Noah added he would need more time and work to recover completely from the injury that occurred during the NBA playoffs.
It's still unclear whether San Antonio Spurs guard Tony Parker will be able to play for France after a scratch to his cornea suffered in a bar fight involving singer Chris Brown and members of hip-hop star Drake's entourage in New York City.
France's first game is against the United States on July 29.