She studied acting under the tutelage of director Soja Jovanović who gave Lončar her film debut—an uncredited bit part in 1960's Diližansa snova [sr].

Lončar's acting break came via being cast, alongside two more first-time film performers: twenty-year-old Boris Dvornik and fifteen-year-old Dušica Žegarac, in France Štiglic's Deveti krug, a Jadran Film-produced Holocaust story about a Jewish family from Zagreb.

By the time Deveti krug was released, sixteen-year-old Lončar had already landed her first lead role—the part of a beautiful young girl Sonja Ilić in the teenage comedy Ljubav i moda produced by Avala Film.

Backed by a pop music soundtrack that achieved its own popularity on the strength of the "Devojko mala" track sung by Đuza Stojiljković, the cheeky picture became a commercial smash hit in communist Yugoslavia.

She additionally signed a five-year contract with Avala Film whose chairman, powerful Yugoslav Security Service (UDBA) operative Ratko Dražević [sr] had begun guiding her career.

Although it ended up not quite matching the success of Deveti krug on the festival circuit, Dvoje got very good reviews for its innovative approach as a breath of fresh air in the Yugoslav cinema that up to that point had mostly been making genre films of very specific and rigid structure and narrative.

Franz Antel cast her in the supporting role of Afra in the Austrian movie The Bandit and the Princess [de], marking the first time she took part in a foreign film.

Forced to scramble, Cardiff looked for a local replacement and ended up casting blonde Lončar whose physical features fit the requirements of the Viking woman role.

Lončar's career in the Italian cinema began in 1964 when she was cast by Mauro Bolognini for his segment within La donna è una cosa meravigliosa [it], a three-segment film.

In early spring, Carlo Lizzani's La Celestina P... R... premiered where she had a sizable role followed by a bit part in Gérard Oury's Le Corniaud and a bigger one in Steno's Letti sbagliati.

During the early 1970s, Lončar married the Croatian hospitality entrepreneur (nightclub owner), musician, and socialite Josip "Dikan" Radeljak, having met him in Split and gone through a short period of dating.