The 68-year-old MLA was battling with liver and kidney diseases for the last several months and left behind wife Kalpana D Sangma, three daughters and two sons.
Marak had undergone treatment at the Apollo Hospitals in Chennai a few months ago.
Chief Minister Mukul Sangma in his condolence said the state has lost a stalwart. "His demise will definitely leave a vacuum difficult to fill," Mukul said while condoling the family members.
Former Lok Sabha Speaker and sitting Tura MP Purno A Sangma said, "Marak was a true nationalist and patriot who spent his entire life fighting and struggling for the rights of the common man."
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Acknowledging his contribution towards the betterment of the state, the MP said, "He also spearheaded the movement for Garoland. It is a great loss not just for Garo hills but for the entire state."
Deputy Speaker and Meghalaya NCP President Sanbor Shullai too expressed deep shock.
The lone legislator from his party which has been fighting for a separate Garoland state, he represented Chokpot constituency in South Garo Hills.
Born in April 13, 1947 at Sibbari village, Marak won four times from Chokpot Assembly constituency.
His stint in politics began with founder chief Minister of Meghalaya, Captain Williamson A Sangma. During his student life, he was actively involved for the hill state movement.