Keane has been linked with a move away this season with some doubting his contribution.
But Redknapp says: "Robbie has been great for us, he's got eight goals and his goal for Ireland the other night was fantastic.
"He has been a great signing for us. I hate it when I hear people criticising him because he played a massive part in keeping us up last year.
"It was no coincidence we went on a great run when he arrived back from Liverpool. The atmosphere around the place changed when he came back because of the way he is, he's infectious."