The US flag has been raised over the American embassy in Havana for the first time in 54 years in a ceremony presided by Kerry.
Kerry was the first US secretary of state to visit Cuba in 70 years. The US flag was raised by the same US marines who pulled it down back in 1961.
"The leaders in Havana and the Cuban people should also know that the United States will always remain a champion of democratic principles and reforms," Kerry said during his speech.
"We remain convinced the people of Cuba would be best served by a genuine democracy where people are free to choose their leaders with commitment, economic and social justice," he added.
The top American diplomat was accompanied by a number of US lawmakers and Cuban-Americans who have advocated normalizing diplomatic and economic relations with the island.
US President Barack Obama and his Cuban counterpart Raul Castro announced the historic rapprochement between their two countries in December after 18 months of secret talks between officials from the two nations.