The airline will add flights from its base at Stockholm-Arlanda Airport to the Italian city in October, and flights from Copenhagen to Lisbon in February.
Both services will run twice a week over the winter season and will operate in addition to new ‘Sterling Connect’ services and other seasonal routes including flights from Billund to London, Malaga, Paris and Salzburg.
Commenting on the Lisbon and Milan flights, Ms Carole Arnaud-Battandier, International Marketing Manager at Sterling Airlines said: "Sterling Airlines is delighted to announce the opening of two new routes to Portugal and Italy.
"This is a fantastic opportunity for our Portuguese and Italian customers flying from the main airports of Lisbon and Milan to be able to experience breathtaking visits to these Viking Capitals in Denmark and Sweden."
Sterling announced in May that it would move all its international departures at Stockholm-Arlanda Airport to the recently refurbished Terminal 5.