Bak studied at Aarhus University in Denmark, receiving an MS degree in computer science in 1988 after which he became active in designing and implementing object-oriented virtual machines.

[2] After participating in the design and implementation of the BETA Mjølner System, in 1991 he joined the research group for the programming language Self at Sun Microsystems Laboratories in Palo Alto, California.

In 1994, he joined LongView Technologies LLC, where he designed and implemented high performance virtual machines for both Smalltalk and Java.

[3][4] In 2002, after returning to Aarhus, Denmark, Bak founded OOVM, a company which developed software for mobile phones.

[10] In 2010, after Oracle bought Sun and with Lars Bak working for Google, Oracle sued Google for infringing on several software patents and amongst them was the "Interpreting Functions Utilizing a Hybrid of Virtual and Native Machine Instructions" patent[11] filed by Lars Bak et al.