The 33-year-old actress, who is expecting her first child with her husband, comedian David Cross, rocked a bright pink Planned Parenthood beanie to the massive protest rallies, where she reunited with two of her former Sisterhood of the Traveling Pants co-stars!
Tamblyn first hit up the march in Washington, D.C., where she met up with America Ferrera, who served as a chair for the Women's March on Washington.
Tamblyn and Ferrera posed together for a smiling snapshot commemorating the historic occasion. "Sister for life," Tamblyn wrote in the caption. "For real. Forever. #womensmarch."
While in D.C., Tamblyn also caught up with her friend, comedian Amy Schumer, who came with a group of fellow protestors all decked out in bright orange NASA space suits.
After marching in Capital City, Tamblyn made her way up to the enormous demonstration in New York City, where she joined a group of protesters who marched on Trump Tower.
The actress reunited with Blake Lively, also of the Traveling Pants on-screen family, in the Big Apple, and the pair snapped another heartwarming selfie in front of an enormous crowd of impassioned activists.
"Sister #2 located in NYC march! #womensmarchnyc," Tamblyn wrote in the caption.
Tamblyn, Lively, Ferrera and Schumer were among hundreds of celebrities who took to the streets on Saturday -- alongside an estimated 2.9 million other protesters worldwide -- to stand for women's rights, human rights and political freedom. Check out the video below to see how some other big-name stars contributed to the historical, multi-city rally.