O'Neill replaced Steve Bruce in November after a poor start to the season left the Black Cats with just 11 points from 13 games.
The revival under the former Celtic and Aston Villa coach saw the North East giants flirt with a European spot before ending the season in 13th place.
And club captain Cattermole believes the confidence instilled by O'Neill gave the players the belief to kick-start their season.
"Martin brought a massive lift to the place," Cattermole told the club's official website.
"And if you look at the results after he took over it showed what an impact he had.
"He gave all the lads the confidence boost they needed and the fans got right behind us. With that we went from strength to strength."
Expectations were high around the Stadium of Light after a busy summer in the transfer market, and the 24-year-old reflected on how the team struggled to cope with early-season setbacks.
"Going into the season we signed a lot of good players but sometimes it takes time for them to gel as a team," he added.
"We started great at Liverpool with a draw and played Newcastle off the park only to lose.
"Things like that can change your season and from then on we really struggled to get back on track.
"That resulted in Steve Bruce going, but we knew we had to pick ourselves up. It was the first time I've lost a manager in mid-season and it took a few days to get my head around, but I knew I had to impress again."
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