Colonel Jose Luis Silva Silva, Venezuelan military attache in Washington, said he was breaking with President Nicolas Maduro and supporting self-proclaimed interim President Juan Guaido.
"I'm sticking to the road map of interim president, Juan Guaido," Silva said in a video shared on social networks.
Silva said the roadmap included "the end of the usurpation of executive power", the "beginning of the transition to a new government" and "free and transparent elections for all Venezuelans who wish to participate".
This led the Venezuelan Ministry of Defense to publish a critical tweet on its official account. The tweet showed a screenshot of Silva's video declaring his defection with the word "TRAIDOR".
Also on Saturday, the opposition-controlled National Assembly drafted an amnesty law to protect military personnel wishing to withdraw from the Maduro government. The measure would also offer graces to civilians, politicians, civil servants and military accused under the governments of Hugo Chávez - president from 1999 to 2013 - and Maduro to have committed crimes or to have supported unconstitutional acts.
Legislators could vote on the bill as early as Tuesday.