“This historic event reflects Somalia’s progress in recent years and is another step forward in formalising US diplomatic engagement in Mogadishu since recognising the federal government of Somalia in 2013,” State Department spokeswoman Heather Nauert said in a statement.
“Our return demonstrates the United States’s commitment to further advance stability, democracy, and economic development that are in the interest of both nations,” Nauert added.
The US diplomatic mission for Somalia in recent years has been attached to the US Embassy in Nairobi, Kenya.
“Ambassador Donald Yamamoto and his team look forward to working closely with the people of the Somali federal government to strengthen our already strong bilateral relationship,” Nauert said.
The embassy was closed and American diplomats evacuated during the civil war in early January 1991 in the face of violence and the collapse of the Somali government.
The Horn of Africa country has in recent years faced an uprising by the al-Qaeda-linked al-Shabab armed group, as well as famine and maritime piracy.
While parts of the country are still plagued by violence, a degree of stability in the capital, Mogadishu, has drawn investment from Somalis at home and abroad.
In September, the World Bank approved $80m in grants to Somalia to fund public finance reforms, the first disbursement to the country in 30 years.
The US carries out periodic air attacks in Somalia in support of the UN-backed government and its fight against al-Shabab.
The rebel group withdrew from Mogadishu in 2011, but it retains a strong presence in areas outside the capital.