The Gunners have been in pursuit of the former Lyon midfielder for over a month, and despite Newcastle's determination to retain the 28-year-old, he pushed hard to join Mikel Areta's side on a four-year deal.
Guimaraes scored 31 goals in 195 Newcastle appearances across five seasons on Tyneside, but he's ready for this new challenge, with Arteta aiming to win the UEFA Champions League in 2027 after losing the 2026 final to PSG.
"I felt inside of me that I need a new challenge in my life and I think to be an Arsenal player is going to be an exciting challenge in my life.
"I'm so excited to join. I will give you my best, I promise. I'm your warrior, I'll never give up. Hopefully we can create many, many good memories together."
Guimaraes' simple message focuses on the grit and energy he will bring to Arsenal's midfield alongside Declan Rice with Martin Odegaard, Martin Zubimendi and Eberechi Eze battling for the third spot in Arteta's engine room.
After a limited preseason, he's not expected to feature in Arsenal's home clash with Borussia Dortmund on August 9th, and Arteta could hold him back to face Como three days' later.