He was born in Kranj, then part of the Kingdom of Serbs, Croats and Slovenes in a wealthy and renowned family of Slovene and Yugoslav patriots. His grandfather was a liberal and monarchist politician and mayor of Kranj, while his father was a local entrepreneur.

After the Axis invasion of Yugoslavia, Sirc managed to escape to Switzerland where he established contact with other Yugoslav emigrants. In Summer 1944, after the Tito-?uba?i? agreement, he joined the Yugoslav Resistance and served in the Yugoslav Army in Dalmatia, Croatia and Slovenia until 1945. After the establishment of the Communist regime he joined other liberals and social democrats who tried to form a legal political opposition to the Regime. In 1947, due to his political activity and friendship with Western diplomats, he was trialed in the so-called "Nagode trial" and sentenced to death. His sentence was ultimately commuted to twenty years in prison, of which he served seven, much of it in solitary confinement.He spent his time in assiduous reading; he became an expert in Marxist political and economic thought, while he was also able to read the most up-to-date western, especially English and American economic literature, provided to him by the Slovenian communists in order to translate it for "internal security purposes".

After release, he illegally escaped to Italy with the help of former TIGR member Stanislav Kamen??ek. From then, he moved to the United Kingdom, where he started an academic career. In his various teaching posts since then, including twenty years at the University of Glasgow, Sirc has been a leading expert on socialist economics and communist regimes. He is one of the founders of the Centre for Research into Communist Economies (CRCE) in London and as of 2006 its current director. For many years, he lectured in Political Economy at Glasgow University.

In 1962, Sirc was among the co-founders of the opposition platform Democratic Alternative, together with a group of Serb, Croat and Bosniak pro-Yugoslav emigrants.

Since the fall of the Communist regime in Slovenia, Sirc has been actively present in the Slovenian public life, writing articles, giving interviews and commenting on political developments and economic issues. In the years 1990 and 1991, his opposition to the independence of Slovenia caused some controversy. Sirc supported of a unified and democratic Yugoslavia and although he admitted this solution wasn't feasible at the time, refused to uphold the idea of an independent Slovenia until the outbreak of the Ten-Day war. He then endorsed Slovenia's decision to break from the Yugoslav Federation.

In 1992, he ran for President of Slovenia with the support of the Liberal Democratic Party (LDS), but received less than 2% of the vote. He later claimed that he had been fooled into accepting the candidacy: he believed, according to his account, that the Party had really accepted an economically and politically liberal program, while in reality, he claimed, it remained strongly linked to the former Communist establishment. In fact, as subsequent polls showed, the great majority of the Liberal Democratic Party's voters voted for Milan Ku?an in the presidential elections.

Sirc later sharply criticized both Janez Drnov?ek and Milan Ku?an, accusing them of hindering the development of an Open Society in Slovenia. In the late 1990s, he collaborated with the writer Drago Jan?ar and historians Vasko Simoniti and Alenka Puhar in staging an influential exhibition on human rights violations in Communist Slovenia, called Temna stran meseca ("The Dark Side of the Moon").

In 2004, he was among the co-founders of the liberal conservative civic platform Rally for the Republic (). In the parliamentary elections of 2000 and 2004, he publicly supported the Slovenian Democratic Party. In May 2010, he became a member of the Slovenian Democratic Party.

He lives in Glasgow's West End and regularly visits his homeland.