After graduating from Lahti Polytechnic with a Bachelor's degree in
graphic design in 2005, Pietari worked briefly as a graphic designer before moving to Barcelona where he pursued his career as a professional illustrator. Since then he has been working with wide range of clients in advertising, editorial, products and publishing. Clients include: Penguin Random House, Starbucks, Citibank, The New York Times, The Guardian, Wired, American Express and many more.

Pietari has participated in several group exhibitions around the
world, including the Now Showing Exhibition – Exploring the Lost “Art”
of the Film Poster in London's Cosh Gallery in 2008. His work has been
featured in the 3x3 Professional Illustration Annual and Print
Magazine's European Design Annual in 2007 and in Gestalten's Naïve:
Modernism and Folklore in Contemporary Graphic Design in 2009.
In 2010 Iittala released aseries of dinnerware featuring Pietari's prints and in 2011 and 2015
the Finnish Post released a series of stamps with his designs.

In 2014 Pietari won the Best Book Cover Illustration award in V&A Illustration awards.