Local police said he was driving his Rwandan coach Gervais Hakizimana and a woman near his home village when he lost control of the vehicle, crashing into a large tree.
Kiptum and Hakizimana died at the scene but the woman, 24-year-old Sharon Chepkurui Kosgei Keiyo, survived with serious injuries.
The runner, who clocked three of the seven fastest marathon times in history, had been hoping to become the first man to run the marathon in under two hours in race conditions at Rotterdam in April as well as make his Olympic debut in Paris in July.
Among the tributes was one from World Athletics President Sebastian Coe who said he was “shocked and deeply saddened to learn of the devastating loss” of the athlete and his coach.
He said: “On behalf of all World Athletics, we send our deepest condolences to their families, friends, team mates and the Kenyan nation.
“An incredible athlete leaving an incredible legacy, we will miss him dearly.”
Also paying tribute was Kenyan Sports Minister Ababu Namwamba who said the country had lost “a special gem”, while former Kenyan Prime Minister Raila Odinga said: “Our nation grieves the profound loss of a true hero”.
Hakizimana, a former runner himself, explained the pair first met when he was training by Kiptum’s father’s farm.
Speaking last year, he said: “I knew him when he was a little boy, herding livestock barefooted.
“It was in 2009, I was training near his father's farm, he'd come kicking at my heels and I would chase him away.”
Kiptum competed in his first major competition in 2018 running in borrowed shoes because he could not afford his own but by 2022 he made his name when he ran the then fourth fastest time on record to win the Valencia Marathon on his debut.
He also won last April's London Marathon in a course record of 2:01:25.