Ms McInnes, currently Phoenix chief risk officer, joined the business in 2009, after holding senior positions at Scottish Mutual and Abbey National.
Jim McConville, Phoenix group finance director, will continue in this role and take on additional responsibilities as group director, Scotland.
Two Standard Life Assurance employees are also joining the executive committee. Jonathan Pears, chief risk officer, will replace Ms McInnes as Phoenix group chief risk. John McGuigan, managing director, customer operations at Standard Life, will join as group head of customer.
Andy Moss remains the chief executive of Phoenix Life and will oversee its traditional heritage business of closed-book activity.
Clive Bannister, Phoenix Group chief executive, said: “We are bringing the two firms together by utilising the respective strengths of both. I am especially delighted that Susan is to become the new CEO of Standard Life Assurance.”
Standard Life pensions chief Barry O’Dwyer will join the Phoenix board as a non-executive director. He is remaining on the executive team of Standard Life Aberdeen where he currently runs the pensions business, including the 1825 wealth manager.