The decree comes into force on Tuesday, June 11, the President's Office says.
Social Democratic Prime Minister Algirdas Butkevičius proposed Gustas as candidate for the post a week ago.
Gustas said after a meeting with Grybauskaitė on Monday that they shared the same views on the Economy Ministry's priorities.
Gustas, 54, holds a master's degree in electronic engineering and public administration. He worked as chancellor of the Ministry of the Interior from July 2009 until this month.
Gustas' past career includes working at the Elektra (Electricity) plant in Kaunas, as a physics teacher, at the companies Kapitalinė Statyba, Hastile and Mileta, as a secretary at the Kaunas City Council, and at the Bank of Lithuania's Kaunas unit. Starting in 2003, he held the post of deputy interior minister and state secretary of the Ministry of the Interior.
On May 29, Grybauskaitė signed a decree to dismiss Social Democratic Economy Minister Birutė Vėsaitė from her post due to a possible conflict of interests.