It is the first visit by the European envoys to Tripoli since European Union member states decided to close their embassies in mid-2014 because of unrest.
French ambassador Antoine Sivan, British envoy Peter Millet of Britain and Spain's Jose Antonio Bordallo arrived at Tripoli's Mitiga airport before heading to the naval base where the unity government has set up operations.
World powers see the establishment of the unity cabinet as vital to tackling a raging jihadist insurgency and rampant people smuggling in the North African state.
The oil-rich country has had two rival administrations since mid-2014 when a militia alliance overran Tripoli, setting up its own authority and forcing the recognised parliament to flee to the remote east.
Italy's Foreign Minister Paolo Gentiloni said during a visit to Libya on Tuesday that embassies would be reopened in the capital in "the near future".