"I was able to meet @Pontifex, welcomed him to my district, presented him Oscar's gift & shared a letter re: his case," Mark-Viverito tweeted.
The painting was done by Rivera and given to Mark-Viverito during one of her visits to him in the jail where he has been held for the past 33 years. Mark-Viverito said she has visited him three times so far this year.
President Bill Clinton offered clemency to Rivera in 1999 but he rejected the offer because of some conditions of the deal, which would have required him to remain on parole and for his group to denounce the use of terrorism.
A broadcast of the pope's visit showed Mark-Viverito holding the canvas, walking near the pope and briefly speaking with him.
Mark-Viverito has not been shy about her support for Lopez Rivera. She is not alone, as many other influential Latino elected officials and members of the Puerto Rican diaspora also have expressed support.
"@Pontifex more than gracious w/ his time, his interest piqued when I shared that gift was from a prisoner I visited in jail," Mark-Viverito tweeted.
The speaker, a native of Puerto Rico, recently made headlines after a U.S. Senate candidate from Nevada disinvited her from a fundraiser after learning of her support for Lopez Rivera.
Last year, Mark-Viverito dedicated the city's Puerto Rican Day Parade to the jailed nationalist, after the parade board named her grand marshal.
Mark-Viverito, who was not raised in a religious household but has said she is inspired by the pope's message of reaching out to those who have less, appeared to beam with pride during the exchange.
"@Pontifex asked if I still visited. Said yes. Asked me to thank him. Said I would. As we parted, I asked for a prayer for Oscar," she tweeted.