The Brazil midfielder spent four-and-a-half seasons with Newcastle and became captain of the Magpies.
Arsenal, who ended a 22-year wait for a top-flight English league title last season, did not disclose the exact length of Guimaraes' "long-term" deal.
But British media reports said he had signed a four-year contract with a further one-year option.
"I feel good, I feel amazing. I'm glad for the opportunity," Guimaraes told Arsenal's media channels.
"We have tough games to play this season so the squad is going to be very, very important and I'm hopeful we can achieve our dreams."
The 28-year-old said he'd been enthused about joining Arsenal right from his initial contacts with sporting director Andrea Berta and manager Mikel Arteta.
"Since the first time I spoke to Berta and Mikel I was excited," said Guimaraes. "I just 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 think after playing two World Cups, I'm at the point of my life, I think I need a challenge like this.
"I want to win trophies, I want to make history and I think I'm in the right place to do it. I'm so excited to start."