He took part in the Great War as a soldier in Józef Piłsudski's Polish Legions. He fought in the Polish-Soviet War of 1920. Between 1921 and 1924, he studied at the Academy of Fine Arts in Kraków, and between 1924 and 1927 he continued his studies in easel painting, conservation and wall painting at the Galleria dell'Accademia in Florence. From 1927 to 1930, he lived in France and attended classes with Józef Pankiewicz (professor of the Kraków branch of the Academy of Fine Arts in Paris). In Spain, in 1933, he learnt the technique of making curdybans, becoming a high-class specialist in it. Kątski worked on the restoration of the Wawel Castle, as well as completing a number of polychrome works in Polish churches, including the St Lawrence Church in Chorzów. The artist was a member of the Association of Visual Artists 'Zwornik'. No paintings by the artist from the pre-war period are known. He took part in the September campaign, and after its failure, he reached the United Kingdom via France, where he served in the First Corps of the Polish Armed Forces in Scotland, with an assignment to the museum department.

In 1948, the artist was sent by the Polish government-in-exile to Canada as conservator of the Wawel Treasures (transported there in 1940). He settled in Ottawa and after a year moved to Montreal. Between 1950 and 1954, the artist worked on the polychrome in the Church of Our Lady of Czestochowa and covered the main altar, the two side altars and the pulpit with curds. The result was one of the most beautiful interiors in the churches of the Polish diaspora in North America, which we can still admire unchanged today. In 1954, Kątski worked on the polychrome of St Adalbert Church on Long Island/New York. In 1957, he took a job as a draughtsman at Canadair Aircraft Works, where he worked until 1963.

The artist took part in the exhibition The Polish Artists in Exile Residing in Canada, held at the Montreal Fine Arts Museum in 1950. The following year, he participated in the Exhibition of Slavonic Art at the Slavic Centre at the University Montreal, also shown at McGill University. The Polish Art Exhibition held in 1954 at the Redpath Museum at McGill University presented the major artists of the war wave - Kątski was on the organising committee of the exhibition and showed five of his works. The artist joined the Polish Arts and Crafts Club (a.k.a. Polish Decorative Club), which was founded in 1955. Kątski's works were shown in the Polish booth at the Canadian National Exhibition in 1956, which was prepared by the Polish Decorative Club. The group exhibition, prepared on the occasion of the Congress of the Canadian Polish Community in 1978 in Toronto, was the last exhibition during the artist's lifetime. After his death, his works participated in a group exhibition at Toronto City Hall, in 1992, organised by the Canadian Polish Research Institute.

In his paintings - themes, colours and composition - Stefan Kątski was a faithful disciple of the Post-Impressionists - Józef Pankiewicz and Pierre Bonnard. He was also close to the achievements of Paul Cezanne, from whom he adopted the assumption that in a painting it is not the subject that is most important, but the way in which it is translated into colours and shapes. Hence Kątski's fondness for still life and landscape. Two collections of Stefan Kątski's works have survived: fifteen oils are held by the Polish Scientific Institute and the Wanda Stachiewicz Polish Library in Montreal (all dating from the 1970s), and eight are in a private collection in Montreal (dated from 1942 to 1967, with the painter's personal dedications on the paintings). In April 2017. The Association of the Kątski Family organised a session in Sanok entitled 'The life and work of a Sanockian - Stefan Antoni Kątski'.

The work in the catalogue
Stefan Antoni Kątski, 'Martwa natura', signed [Kątski 1957] in the upper right corner, 90 x 70 cm, from a private collection in Montreal. On a slightly crumpled tablecloth with blue and white stripes lie apples, two green peppers, in a white dish six mandarins, in a brown bowl two yellow and brown pears, on a green plate three pears. The vertical element is a green decanter bursting at the base, climbing upwards. Next to it stands a white cup with an orange border. The whole vibrates with shapes and colours. The agitated tablecloth adds volume to the composition, giving rhythm to the still life. The painting proves the hand of a skilled Post-Impressionist, who has created a clear composition, despite the multiplicity of objects, which conceals order and harmony.