ABC Family announced on Tuesday (October 16) that the Olympic gold medallist will play herself in a third season episode.
Franklin's cameo will see her discuss swimming strategies with Emily (Shay Mitchell) when the two girls meet at The Brew.
The swimmer set a world record during the London 2012 Summer Olympics Games in the 200m backstroke.
She won five medals in all during the Olympics, four of which were golds.
Pretty Little Liars airs Tuesdays at 8/7c on ABC Family.
Watch Missy Franklin set her 200m backstroke world record below (US only):