The "I Am Cait" star took to Twitter to make the official announcement, reported E! online.
"Some days I just gotta say...I love that I'm finally free to be me. #TransIsBeautiful," Jenner wrote.
"I'm finally free to announce my partnership with @MACcosmetics! All sales of our lipstick shade, 'Finally Free,' go towards improving transgender communities. Look for it in April! #MACCaitlynJenner," she added.
All of the proceeds from the 'Finally Free' lipstick will benefit the MAC AIDS Fund Transgender Initiative which works to improve the lives of the transgender community.
The partnership will begin with an April 7 launch on MAC cosmetics' website.
Jenner joins other famous MAC spokesmodels such as Lady Gaga, Rihanna, Nicki Minaj and Fergie in representing the brand.