Before joining Arsenal in August 2021, Ramsdale was relegated from the top flight with Bournemouth and Sheffield United.
But he has played an important role in Arsenal's title charge this season, most recently making a series of vital saves in their 2-2 draw with Liverpool at Anfield in the last game.
"He has been really, really good and probably against the odds," Arteta told reporters on Friday. "Because when you look at his past and where he was coming from, he got relegated twice, it was difficult to imagine it.
"But we saw he had that character, charisma and personality to play for our club and the potential qualities to feed into our way of playing.
"When you see the development he had in the past two seasons I think he is exceptional."
Ramsdale, who has three caps for England, has 12 clean sheets in the Premier League so far, behind only Manchester United's David de Gea and Newcastle United's Nick Pope, who are tied at 13.
Arteta said the club tried to protect Ramsdale when he faced abuse on social media after his arrival, adding that he was facing criticism even before he played his first game for Arsenal.
"It was tough, he needed some support and we had to protect him, but he was ready to handle that," Arteta said.
"He knew that was going to happen, we discussed that before: 'You're coming from this situation, you're going to Arsenal and you're going to have a lot of question marks over your head.' And you have to do that."
Arsenal, who have a six-point lead in the league, travel to West Ham United on Sunday.
