The Inspiration4 crew left on a SpaceX capsule from Florida on Wednesday, and landed off the state's coast after 19:00 local time (23:00 GMT) on Saturday, reports the BBC.
Four parachutes slowed the capsule's descent before it landed in the water, where SpaceX boats sped to retrieve it.
The Inspiration4 team was led by billionaire Jared Isaacman, chief executive of the e-commerce firm Shift4 Payments Inc, who acted as mission "commander".
He had paid an undisclosed sum - estimated by Time magazine to be about $200 million (£145 million) - to fellow billionaire Elon Musk for all four seats aboard the Crew Dragon.
Mr Isaacman was joined by three strangers he had selected - geoscientist and former Nasa astronaut candidate Sian Proctor, 51; physician's assistant and childhood bone cancer survivor Hayley Arceneaux, 29; and aerospace data engineer and Air Force veteran Chris Sembroski, 42.
"That was a heck of a ride for us," Mr Isaacman radioed shortly after landing. "We're just getting started."
The trip marks the third time Elon Musk's company has taken humans to space and back - and another milestone in the space tourism market.
"Congratulations @Inspiration4x !!!" he tweeted after the quartet's safe return.
"Welcome to the second space age," mission director Todd Ericson told a press conference, saying that after this, "space travel becomes much more accessible to average men and women."
Onboard computer systems were in control of the Dragon capsule during its journey, overseen by SpaceX teams on the ground.
The Dragon was not scheduled to go near the International Space Station (ISS), instead of embarking on a "free flight" to a target altitude of 575km (360 miles).
The crew, who underwent six months' training, circled the Earth more than 15 times each day.
Experts gathered data on their blood oxygen levels, sleep, cognitive abilities and other vital signs during the trip, to study the impact being in space would have on non-professionals.
The trip will raise funds for St Jude's Children's Research Hospital, in Tennessee, where crew member Hayley Arceneaux was treated as a child, and now works.
The foursome plan to auction objects they took into space with them, including a ukulele.