"The wealth of the Lebanese prime minister, Najib Mikati, and his family is a result of over 20 years of continuous work in the telecommunications sector," the office said in a statement on Tuesday.
Mikati declared his assets and property to the Constitutional Council of Lebanon before the start of his political career, it added.
In 1982, Mikati, together with his brother, founded a satellite communications firm, and later created the M1 Group, an investment company with assets in South Africa, Europe and the United States.
Mikati served as minister of public works and transport from 1998 to 2004 and headed the cabinet of ministers in 2005 and 2011. His third stint as prime minister began in September.
On Sunday, the International Consortium of Investigative Journalists (ICIJ) unveiled the so-called Pandora Papers, a dossier of more than 11.9 million leaked financial documents exposing the offshore activities of over 300 prominent global political figures. The list includes Mikati, as well as former Lebanese Prime Minister Hassan Diab and the central bank governor, Riad Salameh. According to the ICIJ, Mikati is among Lebanon's wealthiest people, with over $2 billion net worth.