England winger Johnson has penned a new four-year deal that will keep him at the Etihad Stadium until 2016, while Argentina defender Zabaleta has extended his stay until 2015.
While an unquestionable raw talent, Johnson has found himself regularly scrutinised by Roberto Mancini - with the City manager recently publicly criticising the fleet-footed winger - and he had been linked with a move away from the club.
However, Johnson, who has scored nine goals in 66 games for City, insists he never considered leaving the club he joined in a £7 million move from Middlesbrough.
"I wouldn't have signed if I didn't see a big future here," the 24-year-old said. "I'm delighted to sign, I'm just glad it's all sorted out. It was never on my mind when I was playing. You can't let that happen, contracts can take a long time these days.
"I want to become a top player, I want to keep winning things and picking up medals. This is such an exciting time to be at the club, things are moving so fast and there's been something new every day in the two years that I've been here.
"It's great being part of it - my game's improved, I'm playing for England and in the Champions League, that probably wouldn't have happened if I hadn't come here."
Mancini added that he expects him to fulfil his potential, saying: "Adam is a good player for me. I think he can improve a lot, though. After signing a new contract we have time to talk regarding this. I am sure (he is going to get better).''
Zabaleta, an irregular starter but important squad man due to his versatility, was set to be out of contract next year.
"I'm in a very good team, and I try to do my best for the club, the team and the fans,'' the Argentinian told the club's official website. "I didn't think twice, I gave a quick answer because I was so happy to sign."