Zygmunt Mycielski is born on 17 August in Przeworsk as the fourth son of Maria née Szembek and Jan Mycielski. At that time the future composer’s father was managing the Lubomirski Fee Tail. 

The Mycielski family moves to Zarzecze, where Jan Mycielski is to manage the Dzieduszyckis’ estate.

The Mycielskis settle in Poturzyca, Volhynia. Zygmunt Mycielski’s father manages the local estate of the Dzieduszycki family. The future composer’s first memories go back to that period.

​​This region on the Bug River has left me with lifelong memories. This may be because I have never seen it again since that time, since before the First World War. This may also be because it has left in me a memory of a wide and vast land greatly loved by all those who were brought up in Ukraine, Podolia or Lithuania. (Pamiętnik/Memoir)

The Mycielskis decide to settle on their own estate in Wiśniowa on the Wisłok River, Podkarpacie region. 

They arrive in Wiśniowa in early August. The outbreak of the First World War forces them to flee. Through Slovakia and Hungary they reach Vienna, where they spent the following months of the war.

In August the Mycielskis return to Wiśniowa. The composer’s mother wrote in the family chronicle under 20 August 1915: 

After a ten-month stay in Vienna, first at Andrassy Gasse 3 – then at Silbergasse 43 – I spent a month in Kraków with my younger children at the Pusłowskis’ house in Kolejowa Street, and on 20 August we came to Wiśniowa and settled here for good.

Zygmunt Mycielski later recalled:

I remember this return very well. My child’s imagination was fired by stories from the frontline. The garden was cut through by trenches, the house was empty, full of bullet holes, with no windows and no doors. The furnishings, partly dismantled by the servants and peasants, were slowly being returned to their old place. Hidden silver and paintings were discovered, furniture was slowly being restored. My father was rebuilding the damaged estate, life was slowly coming back to what it had been before.

The Kraków pianist Maria Peterówna comes to Wiśniowa in the summer. Her playing makes a huge impression on young Zygmunt. The boy notes down his first compositions and wants to learn music.

That summer there came Wiśniowa the first person who showed me the values of notes, clefs, and principles of harmony. I was thirteen years old. I had already been playing everything “by ear”, I would spend every bit of my free time at the piano. [...] A student from Kraków’s Musical Institute, Maria Peterówna, later wife of Kazimierz Wysocki, gave me these first, so belated lessons, when I was already certain that I would devote my life solely to music. (Pamiętnik/Memoir)

In September Zygmunt Mycielski starts Year Four at the St. Hyacinth Gymnasium in Kraków, ul. Sienna 13. At the same time he begins private piano and music theory lessons with the Kraków pianist and teacher Zygmunt Przeorski.

In May Mycielski goes on a school trip to the Tatra Mountains for the first time. He writes to his mother: 

The Tatras are the most beautiful place I know. (30 May 1925, Jagiellonian Library).

In May Mycielski takes his final high school exams.

In October he begins his studies at the Faculty of Philosophy, Jagiellonian University. He also begins attending Zdzisław Jachimecki’s and Józef Reiss’ musicology lectures as part of the Theory and History of Music Seminar.

Towards the end of the year he starts composition lessons with the Franciscan Father Bernardino Rizzi, a representative of the Caecilian Movement, highly regarded in Kraków. 

In November Mycielski meets Karol Szymanowski. This relationship would be of key importance to Zygmunt’s professional development.

In late January Mycielski visits Karol Szymanowski in Warsaw. The master looks through his compositions and gives him some advice. 

In October Mycielski begins his composition studies at the École Normale de Musique in Paul Dukas’ class. Music theory classes are given by Nadia Boulanger.

In November Mycielski writes to his mother:

– Dukas is Dukas. Chorales. But Boulanger is getting better and better. – Last week we had the first lecture on the history of music with her. She gave students general advice. Above all, again and again, lecture a vue, development de l’oreille in order not to theorise but to hear and remember and then develop a theme on the basis of such a diapason! She was the first to show me how, in all respects, this subject as a whole can give me a system of thinking and an order in the mind. – Above all, an exercise for the mind, perhaps even greater than that of mathematics – and the material to be worked through covers works and disciplines from Plato’s Republic, Pythagoras and the ancients, through the Middle Ages, the Renaissance to Maritain. These are lectures which contain everything, and everything in a system and order, in the clarity and ease of form, on a diapason, routine, pedagogy...(I didn't think such a modest woman could find so much reason, and routine, and breadth of horizon in herself). (10/11 November 1928, Jagiellonian Library).

Mycielski joins the Association of Young Polish Musicians in Paris.

On 17 March Maria Modrakowska (with Susanne Astruc on the piano) performs one of Mycielski’s Triolets for soprano and piano in Paris. It is Zygmunt Mycielski’s debut as a composer.

Premiere of Piano Trio in Paris on 25 March.

In the autumn Zygmunt Mycielski begins mandatory military service in Przemyśl. 

In March, after his release from the army, Mycielski leaves for Vilnius, where he begins working for the Vilnius station of the Polish Radio. He also writes for Kurier Wileński.

In May and June, while staying at Michał Tyszkiewicz’s estate in Orniany, he composes Five Wedding Songs for soprano and piano to words by Bruno Jasieński.

Towards the end of December he returns to Paris and is elected president of the Association of Young Polish Musicians.

A concert of the Association of Young Polish Musicians is held in Paris on 30 January, with the programme featuring works of the association’s members. Mycielski’s Wedding Songs are performed for the first time. After the concert the French reviewer Susanne Demarquez writes: 

I regret to say that I recognise in these young people an irritating unity of thought, combined with an even more regrettable lack of personality. Is it possible that Chopin exhausted all creative forces in Poland for a century to come? I hope not. Yet [...] I see nothing noteworthy. Perhaps with the exception of Mycielski’s 5 Wedding Songs written with gusto, at times even moving. (quoted after R. Suchowiejko, "Muzyczny Paryż à la polonaise w okresie międzywojennym. Artyści – wydarzenia – konteksty", Kraków 2020).

Mycielski resigns as president of the Association of Young Polish Musicians and decides to return to Poland for good. He spends the summer in Wiśniowa and in the autumn again begins working in Vilnius.

After Karol Szymanowski’s death Mycielski accompanies the funeral procession from the Polish border to Kraków, where the body is laid to rest at Skałka. He dedicates Lamento di Tristano, which he is composing at the time, in memory of the master.  

In August he moves to Warsaw and begins working as a regular music reviewer for Kurier Poranny.

In the spring he moves to Bukowina Tatrzańska, where he rents a simple cottage. He lives there until August 1939.

After the outbreak of the Second World War Mycielski reports for military duty and takes part in the September Campaign. After its failure he manages – via Hungary, Yugoslavia and Italy – to get to France, where he joins the Polish army units being formed there. 

Mycielski takes part in the fighting on the Maginot Line. On 17 June he is captured by the Germans. He spends the rest of the war in Stalag Xa in Schleswig-Holstein, sent to work as a forced labourer in neighbouring farms.