Nelis began his career as a trainee at Ernst and Young (currently EY) in 1993. After completing his traineeship and obtaining his CA (SA), he joined Deloitte USA to further his experience. He has been in practice for over 21 years. In 2007, he obtained an M Com (Taxation) specialising in international tax and was the President of the Northern Region of SAICA representing the profession for a number of years.

In 2009, Nelis became a Partner and director at Grant Thornton Pretoria and eventually SNG Grant Thornton. He has been involved in the audits of corporate entities as well as those of medium and large privately held businesses. He attended specialised global training in servicing Privately Held Clients and their owners in Sweden and also in Ireland. He has acted as Auditor, Accountant and Advisor to many businesses and their owners.

Nelis headed up the outsourced accounting division from 2018 and was one of the founding members of the division specialising in Cloud-based services based on the Xero platform. Cloud based accounting and other Artificial Intelligence based services form part hereof.

He joined the Investhouse Group in 2022. He specialises in all aspects of advice including outsourced CFO services, cloud-based services and direct and indirect tax advice to both companies and individuals.