The Wearsiders have shot up the table since O'Neill's arrival in December and currently sit 12th in the Premier League after a relegation scrap looked likely under predessecor Steve Bruce.
And Gardner insists the former Leicester and Aston Villa manager has been an inspiration to his players in times of trouble.
He told The Independent: "If you ever need any support, all you have to do is look to the touchline and he's there jumping up and down, kicking every ball, fighting your corner and that's exactly what you want.
"You need a manager like that if you are finding it tough on the pitch. On Sunday [against Newcastle] we got Stephane Sessegnon sent off with more than half an hour to go. You look at the touchline and you see the gaffer jumping up and down, buzzing about and that is what spurs you on.
“I'm a winner and I'm not a quitter. Newcastle fans are booing you and chucking stuff at you in the derby and all you need to do is look on the gaffer.”
Gardner admits he found it tough to settle in Sunderland under manager Steve Bruce, after finding a first-team spot tough to come by.
"I played for Birmingham last year and scored 10 goals,” he said. “I am an attacking midfielder and I have come here because I want to do the same thing and it was hard.
“What was the point in coming up here, training five days a week and then sitting on the bench? I came up here to play games. Yes, I did have a price tag on my head but I wanted to play games.”
Gardner was allowed to leave Aston Villa by O’Neill in 2010 after failing to secure regular football at Villa Park, moving to City rivals Birmingham and the midfielder hailed the move as being vital in his development.
He continued: “He sold me because I needed first-team football. I was in a position where I thought to myself I was good enough to play regularly in the Premier League.
“Not being big-headed, I was too good to play in the reserves and I did not want to be stuck there because what happens after that?
"I wanted to be a Premier League footballer and I got that opportunity with Birmingham which was a great move for me. I did well there and then the opportunity to move to Sunderland came up and I could not turn that down.”
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