The storied spacecraft is carrying a crew of four US astronauts on a 12-day mission to re-stock the orbiting lab, where it is due to dock on Sunday.
The mission marks the end of an era in human spaceflight. The United States will soon have no spacecraft capable of taking astronauts to orbit, leaving Russia's three-seat Soyuz capsule as the sole taxi to the ISS.
At least 750,000 people descended on Florida to catch a glimpse of history, braving snarled traffic and warnings of stormy weather that had briefly threatened to postpone the mission.
Some tourists gathered at the Kennedy Space Center to watch the launch wiped away tears afterward, overcome by the emotion of witnessing the potent blastoff and feeling it rattle their bones and burn their eyes.
Kevin Dang, 32, said the "rumbling was really, really loud and you could feel the ground shake."
Tourist Pete Riesett, 31, described the event as the "best thing ever," and said he felt no sadness for the fast-approaching end of the shuttle program.
"To be honest, I am actually fine with it," he told AFP. "It is time for it to go and it is time for something better to come in its place."
Once the shuttle retires, astronauts will be limited to catching rides to the ISS aboard the Russian Soyuz spacecraft at a cost of $51 million per ticket.
Nostalgia, bitterness and sorrow mingled with pride at Kennedy Space Center as thousands of workers watched their cherished spacecraft sail into the skies.
As many as 8,000 people are being laid off with the closure of the shuttle program.
"So many folks are losing their jobs. They do it because it is their passion. We have really, really good people," lamented astronaut Terry Virts.
"The sad part about it is that we won't have an American ability to launch astronauts anymore."
Former president Richard Nixon ordered the shuttle program in the 1970s, and the first shuttle mission was launched in 1981.
In the days leading up to Atlantis's last launch, NASA fended off criticism over the lack of an immediate successor to the shuttle and showed off the design of the Orion space capsule, the basis for a multipurpose crew vehicle that may someday travel to deep space.
"I don't see this is as the end of the golden era," said NASA associate administrator for space operations Bill Gerstenmaier after the launch. "I see it as a transition."
Private companies like SpaceX, Boeing and Sierra Nevada are competing to become the first to build a next-generation space capsule to take astronauts and cargo to the orbiting research lab.
But those plans are not likely to come to fruition before 2015 at the earliest.
President Barack Obama "honors the shuttle program and the service of everybody who has worked on it over the years," said White House spokesman Jay Carney at a briefing in Washington.
"The president has laid out an ambitious agenda, an ambitious vision for human space flight that will take American astronauts beyond where we've been ever before, with the ultimate goal being a human mission to Mars."
Asked by a reporter when that might be, Carney answered: "Well, I think if we knew that, there wouldn't be the challenge, would it?"
Of the six US space shuttles, the prototype Enterprise never flew in space, Challenger exploded after liftoff in 1986 and Columbia disintegrated on its return to Earth in 2003. Fourteen crew members died in the two disasters.
NASA plans to send the remaining three shuttles in the fleet -- Discovery, Endeavour and Atlantis -- to museums across the country to go on permanent display.
Copyright APP (Associated Press of Pakistan), 2011
Copyright AFP (Agence France-Presse), 2011