The 27-year-old moves to Scotstoun after impressing for the Griquas in this season's Currie Cup, helping the men from Kimberley to their fifth title and starting in the 23-16 victory over the Pumas in the final.
A product of Selborne College and Maties Stellenbosch, Lyons made 26 appearances in total for the Griquas, having previously represented the Stormers and Western Province.
Lyons' form also saw him added to the Lions squad for the 2025/26 season, featuring in the Johannesburg-based side's clash with Newcastle Red Bulls last December.
The prop has arrived in Glasgow, with his contract running until the start of the Guinness Six Nations in February.
"I'm incredibly excited and grateful for the opportunity to make the move from the Griquas to Glasgow Warriors," Lyons told glasgowwarriors.org.
"This is a special next step in my career, and I'm looking forward to embracing the challenge, learning from the environment, and contributing to the team in every way I can.
"I'm ready to bring my physicality, adaptability, and work ethic to the group, while doing everything possible to help the team achieve its goals.
"I'm truly thankful for the trust and opportunity, and I can't wait to get started, represent Glasgow Warriors with pride, and give everything I have for the jersey."
Head Coach Franco Smith added: "With both Nathan McBeth and Rory Sutherland currently in the Scotland setup, we are pleased to be able to add a player and a person of Leon's calibre to our playing group to provide us with further depth in the front row.
"He is someone who is keen to work hard and become a Glasgow Warrior, with his enthusiasm to get involved evident throughout our discussions to date.
"He will also provide a strong role model for our young front-rowers such as Jake Shearer and Ollie McKenna, giving them an additional experienced professional from which to learn as they continue to develop."
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