The Gunners on Wednesday, agreed a £25million fee with Celtic for the left-back.
The 22-year-old has signed a five-year contract and will wear the No.3 shirt.
“It feels great. I’m delighted to be here.
“Obviously I’m injured now, but I’m just looking forward to getting back on the pitch, training and getting involved with the squad,” Tierney told Arsenal’s official website.
On having to leave Celtic, his boyhood club, he added: “It was the hardest decision in my whole life that I’ve had to make.
“I had to speak to my family and my close friends and my agent as well because it’s a hard decision to leave a club that you love so much. People need to know that as well.
“I feel Arsenal is a massive club and it’s a great opportunity for me as well. I’m delighted to be here.”
