The Seoul parliamentary source said Kuala Lumpur sent confirmation the oldest son of former leader Kim Jong Il was killed, South Korean news service News 1 reported.
Kim Jong Nam drew international attention in 2001 when he was arrested in Japan while attempting to visit Tokyo Disneyland with his son on a fake Dominican Republic passport.
Since the incident, he had been leading the life of an exile and is believed to have resided for a time in China, Southeast Asia and Europe, South Korean network KBS reported.
He was once spotted in France, where his son Kim Han Sol was attending school.
In 2012 Kim Jong Nam published a memoir that included a scathing criticism of the hereditary rule of the Kim family.
He was spurned for the succession, and his father appointed his younger half-brother Kim Jong Un before his death in 2011.
Japanese journalist Yomi Koji, who authored My Father, Kim Jong Il, and I, said Kim Jong Nam considered "helping" his half-brother rule North Korea but changed his mind after he realized he had been "neglected" by the regime.
He never sought asylum in South Korea like some of his relatives, including Lee Han-young, the nephew of his mother, Sung Hye-rim. Lee was assassinated on South Korean soil in 1997.
South Korean politicians are issuing responses to news of the killing, Yonhap reported Tuesday.
Oh Shin-hwan, a spokesman for the conservative Bareun Party, said members of his party "cannot help but be dismayed at the 'fearpolitik' of Kim Jong Un" while urging a closer examination to see whether the incident would affect national security.
Kim Kyung-jin, a spokesman for the progressive People's Party, said efforts should be made to avoid escalating tensions in the region.
He said Seoul should "urge the Malaysian government to promptly identify the truth of the case and present it to the international community."