The 25-year industry veteran will oversee finance, accounting and acquisition strategy and report to Scott Friedlander who joined the company in mid-January.
Tommer brings experience in driving organic growth, strategic acquisitions and financial compliance, Friedlander said in a release.
Previously, Tommer served as vice president of finance at Vangent, where he oversaw financial reporting, treasury and risk management.
General Dynamics completed its $960 million acquisition of Vangent in September 2011 and integrated Vangent into the information technology unit.
He also served as senior vice president of finance at SI International for 10 years, where the company says he integrated nine acquisitions and helped increase revenue to $600 million.