The duchess spoke at a Women@Spotify event in Los Angeles, where she met female employees of the audio streaming platform.
The T-shirt is from Canadian Etsy story K&R World Design and is currently available to buy from $28.22. Meghan chose the black cotton shirt with white writing.
The store has the piece listed as a "Mahsa Amini T-shirt" and describes it as a "women's rights T-shirt. Be the voice of Iran" with the Farsi slogan, "Zan Zendgi Azadi", written in English. K&R World Design is also selling T-shirts with the slogan written in decorative calligraphy.
Mandana Dayani, the president at Archewell, the Duke and Duchess of Sussex's non-profit organisation, shared a photo with Meghan at the event with the NGO's executive vice president, Ashley Momtaheni Hansen. Both Dayani and Hansen are Iranian.
"Women. Life. Freedom. Allies have shown up in so many forms over the past month since the death of Mahsa Amini," Dayani wrote on Instagram. "I am so grateful to work with incredible women like Meghan and my fellow Iranian colleague and friend, Ashley Momtaheni, as we continue to highlight the bravery and courage of the women and young girls on the frontlines of one of the most important feminist movements of our lives.
"At an event today, Meghan spoke about the revolution being led by women and young girls in Iran, the courage and bravery they show every day, and their leadership and advocacy of basic human rights: women, life, freedom.
"As an Iranian woman who fled her home country in pursuit of these very freedoms, I could not have been more grateful for how she chooses, again and again, to advocate for women around the world. Proud day at Archewell, and especially for me and Ashley Momtaheni."