Herman has been in investment management since 1985, holding senior positions in several asset management companies. He began his career when awarded a bursary from Old Mutual, studying a BBus Sci majoring in Actuarial Science, Statistics (Honours) and Economics. After a period at Old Mutual, he co-founded an asset management company.

In 1993 Herman started the first index tracker fund, the Composite Unit Trust, in South Africa. This was sold to Investec, which he joined in 1995. He established Investec's international fund management capability, establishing fund structures in Dublin. In 1998 Herman and Guy Toms founded Prescient Investment Management which applies its investment techniques to cash, bonds, equities, balanced portfolios, and asset allocation.