The Irish-qualified 24-year-old joins the province after coming through the ranks at Connacht Rugby.
Born in Bristol, Mullins qualifies for Ireland through his family heritage, with his grandmother hailing from County Cavan.
A versatile back three player with pace and power, Mullins was a key member of the Ireland Sevens team that won the Rugby Europe Sevens Championship Series in 2023.
The back was also a part of the Ireland Sevens team that played in the 2024 HSBC SVNS Series in Singapore and the 2024 Paris Olympic Games alongside Ulster winger, Zac Ward.
Following his involvements with the Sevens game, Mullins made a strong impression for Connacht, scoring a hat trick of tries on his Senior debut against Zebre Parma in December 2024.
Head Coach Richie Murphy is familiar with the talented speedster, having coached him at Ireland U20s.
Commenting on the news, Mullins expressed his delight after signing on to become an Ulster player.
“This is a really exciting move for me, and I was delighted to have this opportunity. I know the coaching staff very well from my time at the Irish 20s under Richie and having worked with Mark Sexton at Connacht.
“I also know Zac (Ward) very well after being around the world with him with the Sevens, so I’m looking forward to being reunited with him as a teammate!
“Having watched Ulster last season, it was clear to see the freedom they are playing in attack and I feel that suits my game. Hopefully I can add to the team and progress as a player.”
Ulster Rugby’s General Manager, Rory Best added:
“We are very pleased to be bringing in a player of Chay’s talent in this summer. With his promise shown in the Sevens programme and at Connacht, he represents a fantastic market opportunity for us.
“We believe his attributes will fit in well with our brand of rugby and the coaches are well aware of his ability having worked with him before.
“His versatility will be a welcome addition into our backline, and he will add strong competition for selection.”