Sony has said it disagrees with the decision and is planning to appeal.
Personal information including customers' payment card details, names, addresses, email addresses, dates of birth and account passwords were exposed.
Sony temporarily shut down the network, a system that links gamers worldwide in live play, after discovering the massive security breach.
David Smith, ICO deputy commissioner and director of data protection, said: "If you are responsible for so many payment card details and log-in details, then keeping that personal data secure has to be your priority.
"In this case that just didn't happen, and when the database was targeted - albeit in a determined criminal attack - the security measures in place were simply not good enough."
The company said at the time that personal data from 77 million users of Sony's PlayStation network had been compromised, and users were all asked to change their passwords following the breach.
Mr Smith added: "There's no disguising that this is a business that should have known better."
"It is a company that trades on its technical expertise, and there's no doubt in my mind that they had access to both the technical knowledge and the resources to keep this information safe."
After the fine was announced, a spokesman for the electronics giant said: "Sony Computer Entertainment Europe (SCEE) strongly disagrees with the ICO’s ruling and is planning an appeal.
"Criminal attacks on electronic networks are a real and growing aspect of 21st-century life and Sony continually works to strengthen our systems, building in multiple layers of defence and working to make our networks safe, secure and resilient.
"The reliability of our network services and the security of our consumers' information are of the utmost importance to us, and we are appreciative that our network services are used by even more people around the world today than at the time of the criminal attack."
The ICO added that following the breach, Sony rebuilt its network platform to ensure that the personal information it processes is kept secure.
Sony faced heavy criticism over its handling of the network intrusion, as it did not notify consumers of the breach until a week after it began investigating unusual activity.
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