Top US trade representative Ron Kirk said Tuesday that he was stepping down from his position in February.
His tenure was marked by a difficult global economic situation, including calls for more protectionism at home.
"It's very hard to pursue an activist international agenda when there's so much churning in the domestic economy. To his credit, he has maintained an open US. trade policy at a time of great stress," Jeffrey Schott, a senior fellow at the Peterson Institute for International Economics told Reuters.
Despite the difficulties, the former Dallas mayor helped reach free trade deals with Colombia, Panama and South Korea, reported the Associated Press.
He also helped complete a deal for Russia to join the Geneva-based World Trade Organization (WTO).
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"It has been no less than my greatest professional privilege to serve President Barack Obama alongside the dedicated professionals of USTR," Kirk said in a statement, reported Reuters.
Kirk was selected to head the trade agency in 2009.
He became the first African American mayor of Dallas in 1995 and made an unsuccessful run for US Senate in 2002.
The Washington Post pointed out that there are many possible successors, including Fred Hochberg, the chairman of the Export-Import Bank; Jeff Zients, the acting director of the Office of Management and Budget; and Francisco Sanchez, who is Commerce undersecretary for international trade.