Redknapp finally landed Parker from West Ham before the close of the transfer window after chasing him for several months.
The Spurs boss admits a lot of people at the club were not convinced about signing Parker because of his age and his personal demands and has thanked chairman Daniel Levy for backing his judgement on the midfielder.
"The hardest signing for me was Scott Parker," Redknapp told the Daily Telegraph.
"It wasn't a deal that the club were crazy about, and I could see their point of view.
"Scott had a four-year contract at West Ham and he was on big money, by our standards. Tottenham don't pay the wages that Chelsea or Manchester City do, so there would be quite a gap.
"There was a feeling that bringing in Scott, 31 years of age and with no sell-on value, could be a problem. I argued that it was what he could give us this year and next that could make the difference. Daniel [Levy, Tottenham chairman] backed me on that."
Redknapp admits he had feared for his side after a turbulent pre-season, in which they fought to keep Luka Modric out of the clutches of Chelsea.
"I felt there was a bad feeling around the club," added Redknapp.
"You know when things are not going right: Luka wanting to go, three or four other players not happy, not pulling their weight in training, disrupting a little bit.
"We looked very, very lightweight. It was a team that scared me a little bit. I just knew we needed to get Scott Parker into the team, get Luka's mind right, and then we would be a different team."