Joining outgoing Haitian president Rene Preval at the inauguration ceremony were the presidents of the Dominican Republic, which shares the island of Hispaniola with Haiti, Honduras and Suriname, as well as other Caribbean leaders and representatives of major donor nations.
Former US president Bill Clinton, the UN special envoy to Haiti, led the US delegation. French Foreign Minister Alain Juppe represented his country.
Martelly won a popular mandate in a sometimes turbulent election protected by UN peacekeepers. The vote was steered through by the international community led by the US, which persuaded local electoral officials to rectify several suspected fraud cases.
Among other challenges facing Martelly is a seven-month-old cholera epidemic that has taken almost 5,000 lives since October last year and is still killing sick Haitians. There is a threat the approaching rainy season could revive it.