Pfc. Kimberly Rivera entered her plea Monday and was sentenced to 10 months in prison and a bad-conduct discharge.
The 30-year-old has said she became disillusioned with the U.S. mission in Iraq while serving there in 2006.
During a two-week leave in the U.S. in 2007, Rivera crossed the Canadian border after she was ordered to serve another tour in Iraq. She applied for refugee status but was denied.
She was the first female U.S. Army soldier to flee to Canada to avoid a second tour of duty in the Iraq war.