Das, who had held the seat since 1995 when it was in undivided Bihar, secured 58,112 votes while Roy got 73,945 of the total 173,618 votes.
Congress candidate Gourav Vallabh came third with 18,976 votes.
Das, who had mostly been trailing in the seat since the counting of votes in the five phase Assembly election began on Monday morning, had also asserted the party would return to power even as early trends showed the Jharkhand Mukti Morcha-Congress-Rashtriya Janata Dal maintaining a good lead.
The alliance eventually won 47 seats in the 81-member house, while the BJP was reduced to 25 seats, against the 37 it won in 2014.
Former Minister Roy, whose efforts put two former Chief Ministers Lalu Prasad and Madhu Koda in jail for corruption, had given a tough fight to Das, in an unprecedented trend which was not expected by the Bharatiya Janata Party (BJP) that had put on hold Roy's ticket from Jamshedpur West, leading him to resign from the Ministry and Assembly and confront Das.
A two-time legislator from Jamshedpur West, Roy had, on November 17, quit the Cabinet in which he had held the Food, Public Distribution and Consumer Affairs portfolios and announced his separation from the BJP.
The next day, he filed his nomination as an Independent candidate from Jamshedpur East seat.
Expelled from the BJP for six years for contesting as an Independent, Roy had alleged that he was denied ticket at the behest of Das and had decided to fight from Jamshedpur East in retaliation.
The Jamshedpur East constituency covers one of the two parts of the 'Steel City', a planned industrial town established by Tata Group's founder Jamsetji Tata. The town's economy largely runs on the steel plant and allied activities.
( With inputs from IANS )