The 29-year-old returns to the club from FOSROC Super Series side Ayrshire Bulls, having been training with Smith's squad at Scotstoun throughout the 2023/24 campaign to date.
Stewart made 48 appearances in his first spell at Warriors and scored nine tries, most memorably scoring in the 2019 Guinness PRO14 Final at Celtic Park.
In August 2019, he came off the bench against France in a Rugby World Cup warm-up Test at Murrayfield. However, he fell out of favour at Scotstoun and was released in the summer of 2022.
Stewart initially joined Connacht on a six-month contract in the 2022/23 season following his departure from Scotstoun, before linking up with the Bulls.
Warriors are currently running pretty low in the hooking department. Fraser Brown announced his retirement last week, George Turner was injured during the Six Nations, Johnny Matthews damaged his ankle in the win over the Sharks and Angus Fraser is out with concussion. Stewart - nicknamed 'Cheese' - has now been named as a replacement for Saturday's URC match against Zebre.
Smith told The Scotsman: "Four or five months ago I had already foreseen something in the sense that you always carry five hookers and with Fraser not being involved I got to know Cheese and understand where he has come from and what was his background. I watched the game against Leinster in the final where he scored a very good try in 2019. I thought this guy had just been mismanaged for a while and let's get him into our environment.
"That was five months ago and he bought into it after struggling a little bit initially with a calf injury. We integrated him and he's been throwing every week for us, he's lost a lot of weight, he got back in shape and he's looking really good."
Stewart's deal is until summer 2026, a show of faith from Smith who thinks there are other players who've not had opportunities to show what they can do.
"There are a lot of boys out there who got so close but didn't get the opportunity at the right moment," added the coach. "Our environment helps players to be the best version of themselves. That is why we invited the Glasgow district team and the Caledonian Reds district team to train with us over the last few weeks with our Viper/A team in preparation for all these games. We got to see a little bit and the invitation was for them to come in and see what it takes to be a pro.
"Maybe there's somebody still out there who's not had that opportunity but is ready to be unearthed and discovered. Going forward with the Super Series stopping soon there's going to be a lot of opportunity for those players who think they can't make it to come and use an opportunity. And that is what, I think, the Warriors stand for. We want to give every person a chance and influence people's lives."