Growing up in the Belgrade neighbourhood of Dorćol, Lončar got involved with performing at an early age. During the late 1950s she was given on-camera speaking bits in kids' and youth programmes on the recently launched TV Belgrade. She studied acting under tutelage of Director Soja Jovanović who gave Lončar her film debut — an uncredited bit part in 1960's Diližansa snova.

With only two films under her belt, by the end of 1960, 17-year-old Lončar's cinematic profile was raised beyond all expectations. She next got cast as the female lead in Aleksandar Petrović's directorial debut — romantic drama Dvoje — alongside Miha Baloh and Miloš Žutić. Playing the role of mysteriously flirtatious Belgrade girl Jovana Zrnić, she once again got plenty of positive reaction in the press. The movie got released in late July 1961, and the following year got selected for the competition programme at Cannes. 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 mostly made genre films of very specific and rigid structure and narrative. The movie also marked the first time Lončar was officially billed with her nickname Beba rather than her given first name, a practice that would be continued for the remainder of her career.

Lončar's career in the Italian cinema began in 1964 when she got cast by Mauro Bolognini for his segment within La donna è una cosa meravigliosa, a three-segment film. At only twenty one years of age she moved to Rome and continued acting in Italian films.

Year 1965 was a breakout one for Lončar in Italy as she appeared in six films. 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. The late summer saw her in Mario Monicelli's Casanova 70 playing one of Marcello Mastroianni's many love interests in the film followed by Luciano Salce's Slalom where Lončar and Daniela Bianchi appeared as tandem of temptresses weaving their web around the duo of pals, both of whom are married, played by Vittorio Gassman and Adolfo Celi. She rounded the year off with Massimo Franciosa's Il morbidone alongside Paolo Ferrari, Anouk Aimée, Sylva Koscina, and Margaret Lee.

Lončar was married to Croatian businessman and socialite Josip "Dikan" Radeljak. The two met in Split during the 1970s and had a son Leo in 1982. After giving birth for the first time at the age of 39, Lončar decided to end her film career. Towards the late 1980s, the couple separated as Radeljak left Lončar for the younger Actress Ena Begović. Following a bitter court battle, their divorce was finalized in 1994 with Radeljak getting the custody of their only son.

During summer 2000, Lončar started living with Serbian skier Stevan Marinković Knićanin whom she eventually married. In late 2000, she moved from Rome back to her hometown Belgrade where she's been living ever since.[1] Despite not acting for almost 30 years, Lončar is still very much in demand by the Serbian and former Yugoslav media. However, she leads a very quiet, low-key life and rarely makes media appearances. Her latest one was for the 50th anniversary of the release of Ljubav i moda during June 2010.[2]

Before Deveti krug was even released, 16-year-old Lončar landed her first lead role — the part of Sonja Ilić, beautiful young girl in the teenage comedy Ljubav i moda.