The 25-year-old full-back has joined the Buddies on a deal to the end of the season and is poised to make his debut against Dundee United this weekend.
Millar was mulling over a few offers after his contract with A-League Newcastle Jets expired, but it took only a few words from the former Rangers, Celtic and Hibs forward to clinch the deal.
"Kenny Miller was coach at one of the teams I played at in Australia and he had nothing but good things to say about the Scottish league," Millar said. "It was exciting listening to him talking about playing in front of the big crowds. There were a couple of offers on the table but, after a glowing reference from Kenny, my mind was quickly made up."
Millar, who had a loan spell with Shrewsbury last season, says he also spoke to former Australia international Scott McDonald, who enjoyed a distinguished playing career with Celtic and Motherwell, and to Curtis Main, his new St Mirren team-mate who was also at Shrewsbury earlier this year.
Although he was born in Melbourne and is in Scotland for the first time in his life, Millar has plenty of Scottish heritage and hopes to track down a host of cousins once he settles into life in Paisley.
"My grandparents were born here in Glasgow and my parents lived here for a bit so obviously there are links there," he said.
"In Australia you get the big games from Scotland which has a good reputation there so it was pretty exciting when the opportunity came up."
Saints manager Jim Goodwin says he has yet to make a final decision on whether both Millar and fellow newcomer Connor Ronan will make their debuts on Saturday but the Australian is keen to get started.
"I landed a week ago so I'm still acclimatising. Getting to sleep through the night is still a big thing,” he said.
"I've not played a competitive match for two and a half months but I've been training on my own and hopefully I can build some fitness in the next week or two.
"It's whatever the gaffer wants but hopefully I will play some part at the weekend. I'll try and put my best foot forward."
Millar is especially looking forward to running out in front the passionate fans at St Mirren Park, which he says will be a new experience for him.
"When I was at Shrewsbury, there was lockdown and I didn't get a chance to play in front of the fans," he said. "I know they have good support at St Mirren.
"Australia don't have purpose-built stadiums for football so we had 6,000 fans in 40,000 and 50,000-seater stadiums and you don't really get the atmosphere that you get in your little boutique 8,000-seater stadiums where the crowd is really close to the pitch. It will be exciting to play in front of that."