Marek Ałaszewski graduated from the Faculty of Painting at the Academy of Fine Arts in Warsaw, where he was a student of, among others, Jan Cybis, Stefan Gierowski and Aleksander Kobzdej.

He started his musical activity while still a student - as a vocalist and guitarist in the band Pessimości i Bardowie. In 1969, together with Marek Skolarski and Andrzej Poniatowski, he founded the vocal and instrumental group Klan. He was a musician, composer and author of some lyrics. After disbanding the band in 1971, he focused on his artistic activities, although he did not give up on music. The Klan was reactivated in 1991.

 Until May 2016, he performed and was active as a composer and painter.

Ałaszewski painted landscapes, including: created the so-called "Venetian" series. His works show the influence of impressionism. The strong points of the paintings are the colors, harmony of colors and open composition.

Ałaszewski presented his works at collective exhibitions in Poland (Szczecin, 1975; Zachęta in Warsaw, 1978, 1987; Poznań, 1976) and abroad (Barcelona, 1975).

 He also had his own individual exhibitions, including:

 at the Brigitte Wąlfer Gallery in Berlin (1978)

at the "U" Gallery in Warsaw (1986, 1990)

in Kordegarda in Warsaw (1995, 1996, 1999)

in the TPSP "Pałacyk" Gallery in Warsaw (2001)

at the "Wieża" Gallery in Warsaw (2007)

at the Nowolipki Gallery in Warsaw (2009)

at Galeria Lufcik in Warsaw (2018)

Vernissage of the "Travel" exhibition at the Lufcik Gallery, Warsaw, April 26, 2018

Marek Ałaszewski is also the creator of art and music happenings, including: The music of concrete.

Decorations

2022 – Silver Medal for Merit to Culture Gloria Artis

2023 – Gold Cross of Merit "for services to Polish culture, for artistic achievements"