Aarnio studied at the Institute of Industrial Arts in Helsinki, and started his own office in 1962. The following year he introduced his Ball Chair, a hollow sphere on a stand, open on one side to allow a person to sit within. The similar Bubble Chair was clear and suspended from above. Other innovative designs included his floating Pastil Chair (similar to a solid inner tube), and Tomato Chair (more stable with a seat between three spheres). His Screw Table, as the name suggests, had the appearance of a flat head screw driven into the ground. he was awarded the American Industrial Design award in 1968.
Aarnio's designs were an important aspect of 1960s popular culture, and could often be seen as part of sets in period science-fiction films. Because his designs used very simple geometric forms, they were ideal for such productions.
Aarnio later work replaced the use of fibreglass (material that can be dangerous especially for those who are directly involved in its manufacturing) with safer types of plastic. He continues to create new designs, including toys and furniture for children.