Lakshmi Mittal has been appointed as chief executive of newly-formed steel group Arcelor Mittal, in a U-turn on a pledge made at the time of the merger.
Mr Mittal's appointment helps "clarify the leadership" of the group
The former Arcelor chief, Roland Junck, was initially given the post after the 22bn euro ($28bn; £15bn) deal.
But company chairman Joseph Kinsch said Mr Mittal was now taking the role "to clarify the leadership of the company".
Arcelor shareholders accepted the takeover after a drawn-out and acrimonious battle between the firms.
Mittal Steel had said it would keep an Arcelor figure in the top job as it tried to limit political opposition to the deal.
But Mr Kinsch said: "It had become clear over the past months that the interests of the company were not best served by the previous structure."
Mr Junck will remain a member of the board and will act as an adviser to Mr Mittal.
The group, which is three times larger than its nearest rival, said it had sales of $22.1bn in the three months to September.
It added that the integration of the two groups was progressing well.