President Barack Obama said it was a "step towards a more normal and productive relationship".
But he may face a battle in Congress where some Republicans are opposed to his dealings with the communist island.
The new ambassador, Jeffrey DeLaurentis, had been working at the new US embassy in Havana, which opened in July last year.
President Obama said there was "no better-qualified public servant".
President Obama and Cuba's President Raul Castro have begun to reignite the diplomatic relations that were broken off in 1961 after the Caribbean island's communist revolution.
What next for Washington and Havana?
What is behind the US-Cuba thaw?
In pictures: US-Cuban relations
Restrictions on flights have been lifted but the US embargo on Cuba remains in place.
Republican Senator Marco Rubio, who is Cuban-American, has previously said the improved relations will go "a long way in providing the economic lift that the Castro regime needs to become permanent fixtures in Cuba for generations to come''.
The US has appointed its first ambassador to Cuba in 55 years as relations between the countries thaw.