Pregnant with her second child, Portman glowed as she spoke to volunteers about the importance of signing up voters. She rocked a pale pink long-sleeve dress with a girly, ruffled hemline for the occasion, completing her look with black tights and pointy lace pumps.
Republican presidential hopeful Donald Trump also made appearances in the area, as the deadline to register in Pennsylvania, a major battleground state, is Tuesday. Clinton's first post-debate appearance was in Detroit, Michigan.
A fan tweeted the tail end of Portman's chat with volunteers, where she noted that they were "right on the finish line."
Not only is Portman stumping for a former first lady, she's playing one on the big screen as well: the famous Jackie O.
The Black Swan star recently spoke with ET's Cameron Matthison at the Toronto International Film Festival, where she admitted that it was tough to play one of the most popular first ladies of all time in her upcoming biopic, Jackie.
"It was really, really scary because, of course, people really know her and have an idea about her, so there's a big pressure to match the way of speaking and the look and the way of moving and everything," she admitted. "But it was nice to be led by Pablo [Larrain], the director of that film, who really allowed me to take it to personal places."