Cornick joined the board in 2004 and became chairman in January 2009.
Simon Troughton, currently senior independent non-executive director, will take up the chairman role.
Director Jim Pettigrew will also step down from the board on 23 April 2016, having served since April 2010.
The news coincided with a trading update from the company revealing assets under management are up to £290.6bn ($414bn) from £283.7bn on 30 September 2015.
Net outflows continued at pace however, with £9.1bn being shed in Q4. This was an improvement on the quarter to 30 September 2015, during which the company lost £12.7bn in assets.
The company warned that the “flows outlook remains difficult and market volatility continues".
"During the quarter we added to the business further, completing the acquisitions of Arden and Advance, followed by Parmenion in early January,” said chief executive Martin Gilbert.
“Like the rest of the industry we continue to contend with the structural imbalances of the global economy and the cyclical slowdown in emerging markets, as well as the impact of falling oil and commodity prices. Despite the day-to-day fluctuations in investor sentiment we remain focused on those issues that we can control.”
“We are committed to our fundamental approach to investing, managing the business efficiently with a keen focus on costs and most of all striving to deliver the long-term returns that our clients and shareholders have come to expect from Aberdeen,” Gilbert continued.
"Our increasingly diversified business model and strong balance sheet mean we are well placed to navigate the current difficult market conditions offering a wide range of investment capabilities for investors."