Published Wednesday, 11 May 2011
Mr Kelly was appointed by US Secretary of State Hilary Clinton in 2009.
He was responsible for helping to create hundreds of jobs in Northern Ireland and attracting some of the world's leading companies to the region.
In a statement, Mrs Clinton said: "During his time as Envoy, Declan has helped our friends in the Northern Ireland Executive and Assembly, Invest NI, and the business community make Northern Ireland one of the best per capita attractors of investment in the world.
"The United States will continue to work with Northern Ireland to expand the opportunities Declan has fought so hard for, and I know he will remain a passionate advocate for the people of Northern Ireland."
First Minister Peter Robinson and Deputy First Minister Martin McGuinness have thanked Mr Kelly for his efforts in helping to regenerate the local economy and for his assistance in securing foreign direct investment.
Mr Robinson said: "The assistance and advice that Declan has provided has been invaluable as we have set about the task of rebalancing Northern Ireland's economy.
"In recent times we have created more jobs than ever before at a higher level than ever before, Declan has worked closely with Invest NI to help make this happen.".
Mr McGuinness said: "Declan Kelly has been a great friend of the peace process and has played a key role in helping the executive attract increasing levels of inward investment over the past couple of years.
"I thank him also for the role he played in the city of Culture 2013 bid and wish him every future success."
Chief Executive of Invest NI, Alastair Hamilton said: "In recent years Northern Ireland has held the distinction of being the only part of the world to have a dedicated Economic Envoy.
"In Declan Kelly, we had someone with immense drive, determination and enthusiasm."