The favourite for the Paris 2024 Olympics was driving from Kaptagat to Eldoret in the Rift Valley of western Kenya around 11:00 pm (2000 GMT) on Sunday when his car came off the road and hit a tree.
Father of two Kiptum and his Rwandan coach Gervais Hakizimana were killed while a woman passenger was seriously injured, police said.
"He lost control and veered off-road entering into a ditch on his left side. He drove in the ditch for about 60 metres before hitting a big tree," said an official police report from Elgeyo Marakwet County where the accident occurred.
It said Kiptum and Hakizimana died on the spot while the passenger Sharon Chepkurui Kosgei was rushed to hospital with serious injuries.
Images on Kenyan media showed the mangled wreck of the vehicle, its windscreen shattered, the roof and doors buckled and almost ripped off.
Kiptum exploded onto the marathon scene when he ran a world record 2:00:35 in Chicago in October, taking 34 seconds off fellow Kenyan star Eliud Kipchoge's previous record.
He was just 23 at the time, and competing in only his third marathon.
Kiptum also won his other two efforts -- his debut in Valencia in 2022 and a follow-up in London the following year.
Kipchoge said he was "deeply saddened" by the death of the "rising star" who surpassed his record.
"An athlete who had a whole life ahead of him to achieve incredible greatness," Kipchoge said in a statement on X.
Kenya's President William Ruto described Kiptum as "one of the world's finest sportsmen who broke barriers to secure a marathon record”.
"An extraordinary sportsman has left an extraordinary mark in the globe," he said on X.
From herding goats just a decade ago, Kiptum had announced he would attempt in April to become the first man to run an official marathon under the mythic two-hour mark.
World Athletics said his debut was the fastest in history and mourned the loss of "one of the most exciting new prospects to emerge in road running in recent years”.
World Athletics president Sebastian Coe said that only last week he had been in Chicago to officially ratify Kiptum's historic time.
"An incredible athlete leaving an incredible legacy, we will miss him dearly," Coe said in a statement.
Faith Kipyegon, who has set world records in the 1500m and the 5,000m, left a wordless tribute on X: three crying emojis and a Kenyan flag.
Kiptum and Kipchoge were anticipated to run together for the first time this summer at the Paris Olympics.
"With the Olympics just days away, we mourn the untimely departure of a promising talent," the president of Kenya's National Olympic Committee Paul Tergat said on X.
"Kelvin's recent ratified record in Chicago showcased his potential for a bright future, representing the next generation of Olympic greatness.”
Kenyan two-time Olympic 800m champion David Rudisha described his death as a "huge loss".
Kiptum hailed from Chepkorio, a village in the Rift Valley that is the heartland of Kenyan distance running, and where ultimately his death occurred.
Ten years ago, barely a teen, he herded goats and sheep and then began following Hakizimana and other runners as they trained in the legendary high-altitude region.
By 2019, Kiptum ran two half-marathons in two weeks, going 60:48 in Copenhagen and 59:53 in Belfort, France. He began training with Hakizimana, who stayed in Kenya when the Covid-19 pandemic struck.
Kiptum's death is the latest in a saga of tragedies to hit Kenya's young athletics hopefuls.
In 2011, Kenyan marathon great Samuel Wanjiru died at the same age after capturing the title at the 2008 Beijing Olympics.
According to a pathologist, Wanjiru was killed from being hit on the head with a blunt object.
In 2021, distance running star Agnes Tirop was found stabbed to death at the age of 25 at her house in Iten, near Eldoret.
Her husband Ibrahim Rotich went on trial for her murder in November last year.
At the end of December, Kenyan-born Ugandan athlete Benjamin Kiplagat was found dead in his car near Eldoret with a stab wound to his neck. Two men have been charged with his murder.