He was appointed Postmaster of Albany in January 1816 in the place of his brother Peter P. Dox, who had held the post from 1814 until his death in office on November 21, 1815. In 1821, Gerrit Dox was succeeded by Solomon Southwick.
In August 1823, the U.S. Postmaster General sued Dox for his failure to render accounts and to pay over some monies received. In the suit, it was stated that Dox had become insolvent in 1819.
In 1839, he was appointed a justice of the Justices Court of Albany.
^"From James Madison to Myndert M. Dox, 21 June 1816". founders.archives.gov. Founders Online, National Archives. Retrieved 19 January 2023. [Original source: The Papers of James Madison, Presidential Series, vol. 11, 1 May 1816–3 March 1817, ed. J. C. A. Stagg, Mary Parke Johnson, Katharine E. Harbury, and Anne Mandeville Colony. Charlottesville: University of Virginia Press, 2020, p. 95.]
^"Appointments by the President". Vermont Republican and American Journal. Windham, Windsor and Orange County Advertiser. 9 May 1829. p. 3. Retrieved 19 January 2023.