Mock will replace Jim Leech, who is set to retire at the end of December after six years at the helm of one of Canada's largest pension funds.
"We're the lead in defined benefits pension plan business globally, and I want us to stay there," he said Tuesday.
Mock was hired in 2001 as the director of alternative investments. He was promoted to vice-president later that year, and again to senior vice-president in 2008, taking on responsibility for fixed income assets and strategy, as well as hedge funds and alternative investments.
"I'm looking forward to spending the next seven months with Jim prior to his retirement," he said.
"His wisdom and guidance is going to give me a lot more insight than I may possess now."
In 2003, Mock was reprimanded by the Ontario Securities Commission for failing to properly supervise a fixed income trader while he was president and chief executive of hedge fund manager Phoenix Canada.
The commission said Mock's failure to supervise a trader in any "meaningful" way led to a loss of more than US$125 million and the collapse of one of the Phoenix Group's master hedge funds, the Phoenix Fixed Income Arbitrage Limited Partnership, in 2000.
Mock was ordered to pay $45,000 in investigation costs and prohibited from being a director or officer of an issuer for six years.
Teachers' spokeswoman Deborah Allan said the fund was aware of the situation before Mock was hired and when his name was brought forward as a potential candidate for the chief executive role.
"We went into this situation eyes wide open," said Allan, adding that Mock was never implicated in anything illegal. "This was an oversight issue."
"He accepted that responsibility. It's the reality of being a chief executive officer. He has that behind him now," she said.
The fund, which manages around $129.5 billion in assets, administers the pensions of 303,000 active and retired teachers in Ontario.
Teachers' earned a 13.0 per cent rate of return last year, beating its benchmark of 11 per cent by two percentage points,
The fund's equity investments returned 14.2 per cent for the year to bring the total public and private investments in the asset class to about $59.5 billion at the end of last year compared with $51.7 billion at the end of 2011.
Meanwhile, Teachers' Private Capital investments totalled $12.0 billion at the end of 2012 compared with $12.2 billion a year earlier and earned 18.6 per cent.
Fixed income assets totalled $60.0 billion at year end compared with $55.8 billion at the end of 2011 and returned 5.1 per cent, while commodity investments lost 1.9 per cent but the amount invested grew to $7.0 billion at the end of the year from $5.7 billion at the end of 2011.
Real assets, which included real estate, infrastructure and timberland, totalled $28.7 billion compared with $25.8 billion and earned 14.7 per cent.