Blues boss Steve Bruce said he had finally got the man he has really wanted all summer.
"He has been my number-one target all along and I am sure he will be successful and score goals for Birmingham City," said Bruce.
"But there's no pressure on Clinton because I'm the manager who went out to buy him, it's my judgement on the line.
"He is an exciting talent and he is also young. I'd like to thank the board and we are still hoping for at least another signing to give us that much-needed strength in depth."
Morrison, obviously delighted at the conclusion of the long running transfer saga said. "I'm really happy to be here and the fact Steve Bruce is here was a big influence on my choice. He is a great manager.
"He helped me a lot when he was at Palace and I want to repay him by scoring the goals for Birmingham.
"It is every kid's dream to play in the Premiership and I am going to enjoy it."