The bill was passed as part of the National Defense Authorization Act and now heads to President Joe Biden's desk for his signature.
The landmark NDAA bill takes away the military's authority to prosecute sexual assault and harassment cases after accusations of ignoring complaints and sweeping them under the rug.
MORE COVERAGE: Vanessa Guillén case
"... this is a bittersweet feeling," Guillén's sister Mayra tweeted. "The loss of my sister created the biggest military law change in history. I awaited so long for this day. All our work [paid] off. There's more to come. Amen."
"This bill will finally answer the call for countless survivors of sexual assault and harassment to provide independent prosecution of these crimes," Garcia tweeted last week after the House passed the bill.
According to the criminal complaint, Army Spc. Aaron Robinson dismembered her body and buried the remains near the Leon River in Bell County.
After a massive search, her body was found more than two months later. Robinson shot and killed himself the next day as authorities closed in to arrest him.
Guillén told her family she was sexually harassed but they said she did not report it for fear of retaliation.
After her death, the Guillén family worked tirelessly to pressure the military to make changes.
In Texas, a similar bill called the Vanessa Guillén Act, was also signed back in June and went into effect Sept. 1.
Robinson's girlfriend, Cecily Aguilar, is awaiting trial on charges of tampering with documents or proceedings and conspiracy to tamper with documents or proceedings in connection with Guillén's death.