Uriel Landeros, 22, allegedly confessed to smuggling spray paint into the Menil Museum in Houston and used a stencil to paint a picture of a bull and the Spanish word "conquista" or "conquered" onto a Picasso painting valued in the millions.
The 1929 painting "Woman in a Red Armchair" has since been restored.
Landeros initially fled to Mexico after a cellphone video of him committing the act was posted to Youtube and went viral.
He returned to the United States in January to face charges of committing graffiti with damage costing $20,000 to $100,000 and criminal mischief. In the plea, the criminal mischief charge was dropped, the Houston Chronicle reported Tuesday.
"He was happy with the deal," defense attorney Emily Detoto said. "With five months credit, he may just go in to get classified and immediately be paroled."
Landerson has apologized, saying he hoped people didn't misunderstand his message. He said he "did this to turn heads ... to raise awareness." The report didn't say to what he was trying to draw attention.