In 1973-1978 he studied at the Academy of Fine Arts in Warsaw. He obtained his diploma in the atelier of Professor Stefan Gierowski and an annex to his diploma in the atelier of Professor Halina Chrostowska. For four years he was an assistant of Professor Halina Chrostowska at the Faculty of Graphic Arts and Linocut at the Academy of Fine Arts in Warsaw. In 1978 he was awarded the first prize for linocut at the International Triennial of Graphic Arts in Krakow. In 1979, he was awarded the first prize for young artists and the third prize at the Jozef Gielniak Printmaking Competition for relief printing techniques. In 1980, Pospieszyński's prints were twice awarded the title of "Graphic of the Month" by ZPAP in Warsaw. The artist was a member of the Association of Polish Artists and Designers (ZPAP) from 1978 to 1981, and was vice-chairman of the graphic arts section of ZPAP, Warsaw branch, from 1980 to 1981.

In 1987 he emigrated to Canada and settled in Toronto. He worked as a freelance graphic artist and was employed by the Peel District School Board, teaching art in schools for five years. In 1992 his drawing won an award at the 31st Annual Toronto Outdoor Art Exhibition, in 1993 his work won the Best Drawing Award at the 2nd Indoor Art Exhibition and at the 32nd Annual Toronto Outdoor Art Exhibition. From 1996 to 2001, he directed the PEKAO Contemporary Art Gallery, which under his artistic direction became an important platform for the professional presentation of Polish and Canadian artists. Important exhibitions of Polish artists took place here: Kazimierz Glaz, Jerzy Kołacz, Tamara Jaworska, Andrzej Pawłowski, Kinga Araja.

In 2001, the artist prepared his solo exhibition 'The Quest for Metaphysical Link' at the PEKAO Gallery, which at the same time ended the gallery's activity. The success achieved and the experience gained in running the PEKAO Gallery allowed Pospieszynski to set up his own gallery: from 2001 to 2013, the artist was the director and curator of Peak Gallery. Peak Gallery's profile was to showcase young avant-garde Canadian and international artists. The gallery gained recognition in the contemporary art world strengthening Pospieszynski's position as a respected expert on avant-garde art and curator. Twice the gallery has participated in ARCO - Art Fair in Madrid, as well as in Photo Miami in 2007 and in the Art Fair MACO in Mexico City.

Since 2017, the artist has been the artistic director of Matter Gallery focused on contemporary art from Africa, Asia, the Middle East and South America. In addition to promoting the art of other artists, the artist continues his work in pencil drawing. The surrealist drawings tell existential stories created from different planes, resulting content with a drawer narrative in which the theme of the human condition, the transience of life, the proximity of life and death plays a central role.

In 1995, Andrzej Pawlowski's sculptures with drawings by Zack Pospieszynski and music by Peter Paul Koprowski made up the exhibition 'Calling Dante' shown at the Italian Culture Institute, transferred to Krzysztofory in Krakow and Warsaw in 1996. In 1997, the artist participated in the exhibition 'Eternal Wandering - Year 2000' at Blackwood Gallery in Mississauga. In 1998. 'Drawings and Objects' was a solo exhibition of the artist's work at MEG Gallery in Toronto.

From 1993 to 1996, the artist was a member of the Ontario Society of Artists and served on the society's board of directors. In recognition of his work in the field of promoting contemporary art, the artist has received multiple grants from the Canada Council for projects. Zack Pospieszynski's work has been awarded in Canada: Juror's Choice Award -The Consilium Art Show in Scarborough in 1992; Honorable Mention - 31st Annual Toronto Outdoor Art Exhibition in 1992; Merit CAPIC - National Show, Toronto in 1993; Best Drawing Award - 2nd Indoor Art Exhibition, Toronto in 1993; Award of Merit - 120th Annual Open Juried Show Image 94 OSA, Toronto; First Price in Sculpture - 17th Annual Juried Show of Fine Art - Art Gallery Mississauga in 1994.

Zbigniew Zack Pospieszynski is a curator who realizes exhibitions with a mindset of respect for art, the viewer and the artist. February 2019. Matter Gallery participated in an art fair in South Africa, where a Johannesburg sculptor represented by the gallery was successful. Currently, the artist's new medium is portrait photography, which relates to the fact that the human being is always at the centre of his interests.

Selected exhibitions: Xylon 8, International Triennal Exhibition of Wood Engraving, Switzerland, 1978; IX Exhibition of Graphics, Zacheta, 1981; Modern Polish Graphic, Gulbenkian Foundation, Lisbon, 1981; 33me Salon de la Jeune Expression, Grand Palais, Paris, 1982/83; Metamorphosis - Solo exhibition, Nassjo, Sweden, 1986; The River, Kariya Art Museum, Japan, 1994; Drawings - Solo exhibition, Artview Gallery, Hamilton, Canada, 1994.

Work in catalogue
Zbigniew Pospieszyński, 'The Debate Philosopher vs Lucifer', 1992, drawing, graphite HB, H2, H6. The work is Zbigniew Pospieszyński's characteristic surrealist existential story built from multiple planes. The elements creating the forms on the drawing are human skulls, terrified faces, plant fragments arranged in two profiles of the title locutors and strange tree forms.