Theodore Mathas, 42, will become chairman of New York Life Insurance Company Monday.

Mathas has been president of New York Life, New York, since July 2007, and he succeeded Seymour Sternberg as chief executive officer of the company in July 2008. He now will take the title of chairman, carrying out a succession plan first announced almost a year ago.

Sternberg 65, has been chairman of New York Life since April 1997. After he retires from that post, he will continue to be the 2008-2009 chairman of the Northeastern University board.

New York Life is the largest mutual life insurance company in the United States, with 17,000 employees and more than $248 billion in assets under management.

Mathas, a board member at the American Council of Life Insurers, Washington, has a bachelor’s degree from Stanford University and a law degree from the University of Virginia. He began working in the asset management department at New York Life in June 1995. He became the chief operating officer of the life and annuity unit in April 2001 and was elected executive vice president in January 2004, when he was named co-head of U.S. insurance operations.

Mathas became chief operating office in July 2006. At that time, he also was elected a board member and vice chairman.