Situated in a late 19th century mansion at the foot of Ljubljana Castle which is also home to Ljubljana Puppet Theatre, the theatre is run by the namesake society Šentjakobsko Gledališče, which was founded in December 1920.
The society staged their first theatre show in June 1921 when they put on August Strindberg's The Pelican. The theatre's golden age began after the ensemble moved to its present location in 1932.
The only time that the theatre temporarily closed its doors was during the Second World War after the Italian occupying forces tore down its stage in 1941 and the society committed to a four-year "cultural silence" or boycott of all cultural activity outside the resistance movement.
Members of the ensemble rebuilt the stage right after the war, and resumed regular repertoire.
The centenary celebrations will begin on 12 December 2020, culminating with a series of events between 9 and 18 June 2021, including an exhibition and the release of a collection of papers looking back at the theatre's history, and a panel debate looking ahead.
More detailed programme is yet to follow, but the society's current chairman Janez Vlaj says they are thinking of putting on a new production of The Pelican.
Vlaj, a Supreme Court judge who has been a member of the Šentjakobsko theatre ensemble for years, notes the theatre's relevance and its progressiveness from its earliest period.
In a newspaper review of the 1925 production of The King of Betajnova, the socially critical play by Ivan Cankar, Srečko Kosovel, the avant-garde poet, noted that "if things go on as they are, one will have to go seeing Cankar at Šentjakob's. We cannot see him at Ljubljana Drama any more any way."
Vlaj finds that the Šentjakobsko Theatre has "become part of the city's image so much that Ljubljana would definitely be missing something vital without it – a lack that even those who do not go to the Šentjakobsko might feel."
The ensemble numbers 150 members, amateur actors who come from various walks of life and do not get paid for their work on the stage, but earn their living elsewhere.
Many have in the past joined the ranks of professional actors, including the likes of Stane Sever, Fran Milčinski-Ježek, Bine Matoh, Dragica Potočnjak, Saša Pavček, Nataša Barbara Gračner, Barbara Cerar, Maja Martina Merljak and Jurij Zrnec.
They put on five to six new productions every year in cooperation with guest directors, set and costume designers and dramaturges, including great directors such as Mile Korun, Diego de Brea or Zvone Šedlbauer. Unlike the actors, those get paid for their engagements.
The theatre attracts an audience of about 30,000 a year. The box office accounts for about half of the theatre's budget, with the rest coming from the Ljubljana city and the Public Fund for Cultural Activities.
The theatre produces plays in all theatrical genres, but tends to favour comedy. It was one of the first in Slovenia to put on a musical, which genre remains a box office hit to this day. The ensemble makes regular guest appearances throughout the country and across the border.