Van Biljon co-founded Mosaic Software. Mosaic built the Postilion payment system, the first high-end payment transaction switch for commodity hardware and operating systems (Windows). Mosaic’s investors included GE and Paul Maritz. The company became one of the top three payment processing software vendors in the world and was sold in 2004 to S1 Corp.

Van Biljon worked for Amazon.com where he, along with Chris Pinkham and Christopher Brown, led the team that developed Amazon’s Elastic Compute Cloud (EC2). Willem built the business plan for the service and was responsible for product management and marketing for the public cloud service.

In 2006, van Biljon left Amazon Web Services and later started a venture with Chris Pinkham. The company, Nimbula, was focused on Cloud Computing software and was funded by Sequoia Capital and Accel Partners. In March 2013, Nimbula was acquired by Oracle Corporation.

After Nimbula, Van Biljon joined takealot.com, the largest e-commerce retailer in South Africa where he served as Co-CEO and CTO from 2014 to 2017.

Van Biljon is also an advisor and board member to a number of technology companies.

Van Biljon co-authored seven patents in cloud computing including “Managing Communications Between Computing Nodes”, “Managing Execution of Programs by Multiple Computing Systems”.