Crew Dragon capsule, dubbed Resilience, parachuted into calm seas about 9am AEST on Sunday, following an automated re-entry descent, SpaceX showed during a live webcast on its YouTube channel.
Within an hour the four smiling crew members were seen emerging one by one from the capsule's side hatch after the vehicle, visibly scorched on its exterior, was hoisted from the ocean to the deck of a SpaceX recovery vessel.
Each of the four stood on the deck for a few moments in front of the capsule to wave and give thumbs-up to the cameras. Each was then escorted to a medical station onboard for check-ups they were to undergo at sea.
Afterward, the amateur astronauts were to be flown by helicopter back to Cape Canaveral for reunions with loved ones, SpaceX said.
The return from orbit followed a plunge through Earth's atmosphere generating frictional heat that sent temperatures surrounding the outside of the capsule soaring to 1927C. The astronauts' flight suits, fitted to special ventilation systems, were designed to keep them cool if the cabin heated up.
Applause was heard from the SpaceX flight control centre in suburban Los Angeles as the first parachutes were seen deploying, slowing the capsule's descent to about 24km/h before splashdown, and again as the craft hit the water.
The astronauts were cheered again as they stepped onto the deck of the recovery ship.
First out was Hayely Arceneaux, 29, a physician assistant at St. Jude Children's Research Center in Tennessee, a childhood bone cancer survivor herself who became the youngest person ever reach Earth orbit on the Inspiration4 mission.
She was followed in rapid succession by geoscientist and former NASA astronaut candidate Sian Proctor, 51, aerospace data engineer and Air Force veteran Chris Sembroski, 42, and finally the crew's billionaire benefactor and "mission commander" Jared Isaacman, 38.
SpaceX, the private rocketry company founded by Tesla Inc electric automaker CEO Elon Musk, supplied the spacecraft, launched it, flew it from the company's suburban Los Angeles headquarters and handled the recovery operation.
The Inspiration4 team blasted off on Wednesday from the Kennedy Space Center in Cape Canaveral atop one of SpaceX's two-stage reusable Falcon 9 rockets.
Within three hours the crew capsule had reached a cruising orbital altitude of just over 585km - higher than the International Space Station or Hubble Space Telescope, and the farthest any human has flown from Earth since NASA's Apollo moon program ended in 1972.
It also marked the debut flight of Musk's new space tourism business and a leap ahead of competitors likewise offering rides on rocket ships to well-heeled customers willing to pay a small fortune to experience the exhilaration of spaceflight and earn amateur astronaut wings.
"That was a heck of a ride for us," Isaacman, chief executive of the e-commerce firm Shift4 Payments Inc, radioed from inside the capsule moments after splashdown. "We're just getting started."
He had paid an undisclosed but reportedly enormous sum - put by Time magazine at roughly $US200 million ($A275 million) - to fellow billionaire Musk for all four seats aboard the Crew Dragon.
Isaacman conceived of the flight primarily to raise awareness and donations for St. Jude, one of his favourite causes, where Arceneaux now works.
The Inspiration4 crew had no part to play in flying the spacecraft, which was operated by ground-based flight teams and onboard guidance systems, even though Isaacman and Proctor are both licensed pilots.
The successful launch and safe return of the mission should boost the fledgling astro-tourism sector.
SpaceX already ranks as the most well-established player in the burgeoning constellation of commercial rocket ventures, having launched numerous cargo payloads and astronauts to the space station for NASA.
Two rival operators, Virgin Galactic Holdings Inc and Blue Origin, inaugurated their own space tourism services in recent months, with their respective founding executives, billionaires Richard Branson and Amazon.com founder Jeff Bezos, each going along for the ride.
Those suborbital flights, lasting a matter of minutes, were short hops compared with Inspiration4's three days in orbit.
AAP with The Project