Sebastian commenced his investment management career at Bell Canada pension fund in 1971 as Investment Analyst, Canadian Equities. In 1973, he was appointed Manager, Canadian Equities. During his first year as Manager, he recommended a long-term policy commitment towards smaller sized Canadian growth stocks as part of the overall Canadian equity investment policy.
In 1977, he was appointed Assistant Director, Financing and later, Assistant Director, Financial Analysis in the Bell Canada Finance Department. Early in 1979, he became a partner of LRM Investment Management Limited. At LRM he continued to develop his expertise in mid and small-cap Canadian equities.
Late in 1984, Mr. van Berkom was invited by Montreal Trust to become one of the founding partners of Montrusco Associates Inc. in Montreal and was appointed Vice-President and Director. His prime investment management responsibility was to manage the Montrusco Select Canadian Small Cap Growth Fund.
In April 1991, he sold his significant shareholding in Montrusco to build VBA into a specialized small-cap investment management company. He is a member of the Montreal Society of Financial Analysts, the Acorn Society, the Cercle finance et placement du Québec, and he is on the Securities Review Board of the Canadian Shareowner Association.
In 1997, Mr. van Berkom was awarded the Small-Cap Manager of the Year Award at the third annual Canadian Mutual Fund Awards Gala in Toronto. Mr. van Berkom was nominated in 1998 as a finalist at the fifth annual Entrepreneur of the Year Awards in Montreal sponsored by Ernst & Young and others.
On November 25, 2003, Mr. van Berkom endowed the Van Berkom Chair in Small-Cap Equities at the John Molson School of Business at Concordia University.
In September 2005, Mr. van Berkom was appointed member of the Board of Directors of the Institute for Governance of Private and Public Organizations.