The 30-year-old has made 47 appearances for the men in black since joining in the summer of 2021, having come through the ranks at Edinburgh. He made his Glasgow Warriors debut in October 2021, coming off the bench in a victory over the Hollywoodbets Sharks at Scotstoun to become Warrior #335.
Equally comfortable across the back-row, Miller scored his first try for the club in memorable style, sprinting over from 40 metres in a dramatic 12-11 win over Aviron Bayonnais in December 2023.
His versatility has been on display throughout the 2025/26 campaign, including his first senior start in the second-row during the Plaster It Purple win over Cardiff at Scotstoun a fortnight ago. He then returned to the back-row in last weekend's victory away to Ulster, helping secure top spot in the BKT URC standings.
Away from matchdays, Miller has also contributed to Glasgow Warriors' women's squad during their 2025/26 Celtic Challenge campaign, serving as lineout coach for Lindsey Smith's side.
A product of Musselburgh and Preston Lodge, Miller represented Scotland at U20 level alongside future Glasgow Warriors team-mates including Zander Fagerson, George Horne, Scott Cummings and Adam Hastings in 2015 and 2016. He was part of the Scotland U20 side that claimed a first-ever win over Australia at the 2016 World Rugby U20 Championship.
Miller also earned distinction in the shortened format, becoming a key figure in the Scotland 7s setup between 2017 and 2020.
"I'm really excited," Miller told glasgowwarriors.org following the announcement.
"The momentum we have here as a squad is brilliant, and I've loved contributing to this group throughout the last five years. I'm looking forward to continuing to get my head down and do my bit for the boys.
"Any opportunity that's presented to you, you have to take with both hands, especially with the calibre of forwards we have here at Scotstoun. We've got such a good group of players here who are always pushing each other forward, so I'm happy to do whatever role is required of me to help the team succeed.
"For me personally, the more I understand something, the more dedicated I am and the more I throw myself into it. The detail that Franco and the coaches provide, therefore, is so good. I know exactly what role I'm fulfilling each time I run out, and that's down to the work that goes on behind the scenes from everyone here during the week.
"I'm also really excited by the group of young players we've got coming through the ranks here, too. When I was starting out as a young professional, I was lucky enough to have a good group of senior pros that helped me form good habits and helped me develop. If I can do the same thing for the young guys here, then I'm more than happy to do so.
"Next weekend is going to be a massive match, and it's amazing to have these big knockout games at Scotstoun. Every time we play in front of our supporters, the place is absolutely rocking - we now need to put our best foot forward and put out the best performance that we can."
Head Coach Smith added: "Ally's work ethic and diligence to becoming the best version of himself has been evident throughout his time with us, and makes him a real asset to our squad.
"His work in training and off the field that goes unseen by supporters helps to put his team in the best position possible, whilst he acts as a strong role model for our young forwards coming through the system.
"He has shown that he is willing to do whatever it takes to help his team succeed, and we look forward to continuing to work with him."