He also studied architecture (1927–31) at the Academy of Fine Arts Zagreb, in the studio of Drago Ibler and in 1931 joined the progressive group founded by Ibler, the Earth Group.
Ironically, however, he became a sought-after specialist in the design of luxury villas in Zagreb, and was thus marked as a hypocrite.
In 1942 he converted the circular Arts Pavilion, Trg žrtava fašizma, Zagreb, designed by the sculptor Ivan Meštrović, into a mosque by adding three free-standing minarets around the body of the central cylinder and designing a new interior richly decorated with arabesques.
The mosque, a monumental and somewhat bizarre addition to the Central European appearance of its surroundings, was demolished in 1949 for political reasons, and Planić was anathemized because of it.
On 30 July 1970 Planić retired but continued with his architectural work.