The year-round link to the British overseas territory from Edinburgh will be joined by a summer route from the capital to Catania in Sicily.
Glasgow will get a new year-round link to Barcelona and summer routes to Dalaman in Turkey and Pula in Croatia.
The expansion is expected to create around 100 jobs - 50 in Edinburgh and 50 in Glasgow.
The routes start in March and April and will operate between two and three times a week.
They will mean a ninth EasyJet aircraft being based at Edinburgh Airport.
The airline has already announced a fifth aircraft for Glasgow.
EasyJet UK country manager Ali Gayward said Gibraltarians had long sought a Scottish link because of their close links.
She said: "We've been asked for a route for a number of years because there are very strong cultural links with Scotland and a lot of ex-pats in Gibraltar.
"There are also financial services firms there which will generate traffic to and from Scotland."
Pilots will need special training to land at Gibraltar airport because of the proximity of the Rock and the frequent foggy conditions, caused by cooler Atlantic air meeting warmer Mediterranean winds.
Ms Gayward said EasyJet was the only airline to offset the fuel it used against carbon emissions.
She said: "It is all we can do today, but it is only an interim step."
She predicted less-polluting hybrid-engined aircraft would not be available until the mid 2030s, and electric planes not until at least 2050.
Ms Gayward said in the interim, more sustainable fuels were not easily available and also "hugely expensive".
She said: "Carbon offsetting is all we can do in the short term."
EasyJet is working with France-based Airbus on a hybrid plane, and with Wright Electric in California on electric aircraft.
The airline's latest expansion north of the Border comes despite the Scottish Government shelving plans to halve air passenger duty, of £13 per passenger on UK and European flights from UK airports.
But Ms Gayward said she believed SNP ministers were still keen to pursue the reduction, despite the need to get EU approval to continue Inverness' exemption from the tax, and the lack of political support in the Scottish Parliament.
EasyJet is Scotland's largest airline, accounting for 25 per cent of all flight seats in Scotland and more than 28 per cent in Edinburgh and Glasgow.
The carrier has flown 97.5 million passengers since it launched its inaugural route between Glasgow and Luton flights in 1995.
Edinburgh Airport chief executive Gordon Dewar said of the new routes: "It's another positive announcement as EasyJet expand yet again at Scotland's busiest airport, basing another aircraft at Edinburgh and providing yet more variety of destinations for passengers.
"Gibraltar provides both leisure and business opportunities while Sicily has been a long sought after destination.
"This expansion is another sign of confidence in Edinburgh Airport from EasyJet."
Glasgow Airport head of aviation Paul White said: "The decision by the airline to continue growth at Glasgow will see these routes support a number of jobs at the airport and add an extra 340,000 seats to EasyJet’s operation.
"We’re particularly pleased to see the return of services to the Croatian town of Pula, which is sure to be popular with Scottish travellers.
“This welcome expansion confirms EasyJet’s strong commitment to Glasgow Airport.”
Malcolm Roughead, chief executive of VisitScotland, said: "Those routes from Barcelona and Gibraltar will open up great opportunities to draw many more visitors from those captive regions and across the east and south of Spain."