Gary Carter received a BA in accounting from Eastern Washington University in 1977, and a Master of Taxation degree from the University of Denver in 1980. He worked as a revenue agent for the state of Alaska, a staff accountant with LeMaster & Daniels, PLLC in Spokane, Washington, and as a senior staff accountant for Peat, Marwick, Mitchell & Co., the predecessor of KPMG, in Denver, Colorado. He has been a certified public accountant since 1977 and is a member of the AICPA and Minnesota Society of CPAs.

After receiving a PhD in taxation at the University of Texas at Austin in 1985, Gary became a tax faculty member at the University of Minnesota's Carlson School of Management, and the Associate Director of the Carlson School's Master of Business Taxation Program. He remained on the tax faculty at the University until 2010. He received multiple teacher-of-the-year awards, and, in 2013, was inducted into the inaugural Carlson School of Management, Master of Business Taxation Program Hall of Fame.

In 1995, Gary began working with the IRS and the Minnesota Department of Revenue to establish a Volunteer Income Tax Assistance (VITA) site at the University, dedicated to helping foreign students and scholars with their federal and state tax filing obligations. In 1996, he launched the predecessor of the U.S. Tax Guide for Foreign Nationals, which has been continually updated since then. It was the first, free comprehensive web-based source of U.S. tax information for foreign nationals, predating even IRS web resources.

At that time the University had 4,000 to 5,000 foreign students, researchers, and visiting faculty on campus from approximately 135 countries. For the next 15 years, Gary annually recruited, trained, and supervised accounting students for the free preparation of thousands of nonresident tax returns for students and scholars. These services were provided, not only to nonresidents at the University of Minnesota but to those at several other area colleges and universities as well.

In 1999, Gary founded a part-time tax practice, and in 2010, GW Carter, Ltd. was launched.