Petr Pokorny was brought up in a family of artists. Having passed his state matriculation at a grammar school in 1951, he studied piano at the Prague Conservatoire with Vaclav Holzknecht and later with Ilona Stepanova - Kurzova. Because of his family background Pokorny was barred from continuing his musical training at the university. He therefore enrolled at Charles University to study natural science, a subject that appeared to be admissible for people coming from his social class. He studied composition mostly in private with Emil Hradecky, Milos Nedbal, Zdenek Hula, and Pavel Borkovec. In the 1960s Petr Pokorny was known to be closely collaborating with the Musica Viva Pragensis ensemble, which frequently performed his own compositions. Furthermore, he was noted for evenings of music and poetry reading in which he would introduce promising young poets. This, however, came to an end after the politically eventful 1968-69 period. Of the following years the composer recalls: "In the early 1970s, when most of my friends had left Czechoslovakia to live abroad, I found myself in utter isolation. My compositions were no longer performed here, I had no more opportunities for organizing evenings of music and poetry reading. My music was not publicly performed again in Czechoslovakia until 1982, at a concert in honour of my 50th birthday." As for the evenings of music and poetry reading, these were resumed in 1989, in a former fortified settlement turned into a community hall in Prague's Chodov suburb. But throughout Petr Pokorny's most difficult years his music, so calm and non-aggressive because genuinely poetic, continued to be well received abroad. Commenting on the performance of Pokorny's composition for bass clarinet entitled "Towards the Centre of Gravity of Sorrow\" given by Milan Kostohryz, together with works by J. K. Vanhal, Brahms, Martinu and Klusak, at the "1975 International Clarinet Clinic" (congress) in Denver, U. S. A., Mary Jungmann wrote in the magazine "The Clarinet": "Of all the works on the programme, Pokorny's composition was the most successful. This fine, melancholy piece was written six years ago for Professor Kostohryz, after the death of his wife. The performing artist's personal involvement certainly contributed to the success of the composition as well."
The music Pokorny composed in the 1960s was characterized by strict adherence to the rules of dodecaphony, but in later years he has seemed to pay less attention to this system. Indeed, this is an era of  "free flow of ideas", as he succinctly described his music in 1990.
Since the political changes in 1989 Petr Pokorny has been able to devote himself to unrestricted artistic and organizational activity. He was involved in the establishment of the new association of composers and musicians Atelier '90, as well as in the birth of the international Musica Iudaica festival. He was active in the OSA composers' organization and a range of others. In the field of composition, he has started to write not only chamber music, but also pieces for larger ensembles (e.g. Lyrical Symphony from 2001). Since 1990 his works have been performed at many concerts and international festivals (Salzburg, the Prague Spring, the Exposition of New Music in Brno, "Contrasts" in Lvov in the Ukraine, the Forfest in Kromeriz and Musica Iudaica in Prague). His Lyrical Symphony got its world premiere at the music festival "Prague Premieres 2006". He was also active as a music journalist.