Gray represented the Philippines in the 2018 Miss Universe contest on 17 December 2018 held at IMPACT Arena, Muang Thong Thani in Nonthaburi Province, Thailand.
During the national costume show presentation, Gray showcased a beaded tribal suit featuring the indigenous tribes of the ancient pagan Filipinos, alongside an oversized Parol painted Christmas lantern pulled by a roller device.
The costume was accompanied by a pre-Christian Shamanic dance of the historical Babaylan paganism.
The costume gained both support and criticism, due to the perceived difficulty of walking and the failure of LEDs to function, whilst Gray cited her scoliosis ailment.

In the pageant's preliminary stages, Catriona Gray did a slow-motion walk, (nicknamed lava walk) on the ramp in the swimwear competition wearing a pink swimsuit, which was praised by supermodels Tyra Banks and Ashley Graham, fashion commentators and Internet viewers.


During the first question and answer round, Gray was asked by host Steve Harvey, "Canada recently joined Uruguay as the second nation in the world to make marijuana legal.
What is your opinion on the legalization of marijuana?"
She responded:
I’m for it being used for medical use, but not so for recreational use.
Because I think if people were to argue: Then what about alcohol and cigarettes?
Well, everything is good but in moderation.


In the final question and answer portion, the top three contestants were asked the same question by Harvey: "What is the most important lesson you’ve learned in your life and how will you apply it to your time as Miss Universe?"
She answered:
I work a lot in the slums of Tondo, Manila and the life there is very... it's poor and it's very sad.
And I’ve always taught myself to look for the beauty in it; to look in the beauty in the faces of the children, and to be grateful.
And I would bring this aspect as a Miss Universe to see situations with a silver lining, and to assess where I could give something, where I could provide something as a spokesperson.
And this I think if I could also teach people to be grateful, we could have an amazing world where negativity could not grow and foster, and children will have a smile on their faces.

At the end of the event, Gray won the competition and was crowned by her predecessor, Demi-Leigh Nel-Peters of South Africa.
She is the fourth Filipina Miss Universe after Gloria Diaz in 1969, Margarita Moran in 1973, and Pia Wurtzbach in 2015.

In beauty pageant history, Gray is the most successful Asian pageant crossover by placing high in both biggest international beauty pageants, Miss World and Miss Universe competitions, becoming the only pageant contestant in the 21st century to have made the Top 5 in both Miss World and Miss Universe, and eventually win either of the world's biggest pageants (in her case, Miss Universe).

On 17 October 2019, Gray attended the 2019 Latin Music Awards at the Dolby Theatre, Hollywood and Highlands in Los Angeles, California where she presented the 2019 "Canción Favorita – Tropical" award for the song "Adicto" to Marc Anthony and Prince Royce.

On 8 December 2019, Gray crowned Zozibini Tunzi of South Africa as her successor at the 2019 Miss Universe competition at Tyler Perry Studios, in Atlanta, Georgia, the United States.

In her capacity as Miss Universe, Gray visited Brazil, Canada, Dubai in the United Arab Emirates, Indonesia, South Africa, Thailand, various cities and states across the United States, and her home country of the Philippines.
Gray represented the Philippines in the 2018 Miss Universe contest on 17 December 2018 held at IMPACT Arena, Muang Thong Thani in Nonthaburi Province, Thailand. During the national costume show presentation, Gray showcased a beaded tribal suit featuring the indigenous tribes of the ancient pagan Filipinos, alongside an oversized Parol painted Christmas lantern pulled by a roller device. The costume was accompanied by a pre-Christian Shamanic dance of the historical Babaylan paganism. The costume gained both support and criticism, due to the perceived difficulty of walking and the failure of LEDs to function, whilst Gray cited her scoliosis ailment.
In the pageant's preliminary stages, Catriona Gray did a slow-motion walk, (nicknamed lava walk) on the ramp in the swimwear competition wearing a pink swimsuit, which was praised by supermodels Tyra Banks and Ashley Graham, fashion commentators and Internet viewers.

During the first question and answer round, Gray was asked by host Steve Harvey, "Canada recently joined Uruguay as the second nation in the world to make marijuana legal. What is your opinion on the legalization of marijuana?" She responded:
I’m for it being used for medical use, but not so for recreational use. Because I think if people were to argue: Then what about alcohol and cigarettes? Well, everything is good but in moderation.

In the final question and answer portion, the top three contestants were asked the same question by Harvey: "What is the most important lesson you’ve learned in your life and how will you apply it to your time as Miss Universe?" She answered:
I work a lot in the slums of Tondo, Manila and the life there is very... it's poor and it's very sad. And I’ve always taught myself to look for the beauty in it; to look in the beauty in the faces of the children, and to be grateful. And I would bring this aspect as a Miss Universe to see situations with a silver lining, and to assess where I could give something, where I could provide something as a spokesperson. And this I think if I could also teach people to be grateful, we could have an amazing world where negativity could not grow and foster, and children will have a smile on their faces.
At the end of the event, Gray won the competition and was crowned by her predecessor, Demi-Leigh Nel-Peters of South Africa. She is the fourth Filipina Miss Universe after Gloria Diaz in 1969, Margarita Moran in 1973, and Pia Wurtzbach in 2015.
In beauty pageant history, Gray is the most successful Asian pageant crossover by placing high in both biggest international beauty pageants, Miss World and Miss Universe competitions, becoming the only pageant contestant in the 21st century to have made the Top 5 in both Miss World and Miss Universe, and eventually win either of the world's biggest pageants (in her case, Miss Universe).
On 17 October 2019, Gray attended the 2019 Latin Music Awards at the Dolby Theatre, Hollywood and Highlands in Los Angeles, California where she presented the 2019 "Canción Favorita – Tropical" award for the song "Adicto" to Marc Anthony and Prince Royce.
On 8 December 2019, Gray crowned Zozibini Tunzi of South Africa as her successor at the 2019 Miss Universe competition at Tyler Perry Studios, in Atlanta, Georgia, the United States.
In her capacity as Miss Universe, Gray visited Brazil, Canada, Dubai in the United Arab Emirates, Indonesia, South Africa, Thailand, various cities and states across the United States, and her home country of the Philippines.
Catriona Gray