Earlier in the month, Sky News confirmed that it had accessed the accounts of 'canoe man' John Darwin and his wife Anne, along with a suspected paedophile.
However, the head of Sky News John Ryley insisted that the action was justified in the "public interest", particularly in the John Darwin case as the information gained was used to help show his wife's involvement in the insurance fraud.
Ryley said that the broadcaster was focused on "responsible journalism" and also questioned the "double standards" of The Guardian, which highlighted the email hacking.
An Ofcom spokesman said that the media regulator is probing the admission in regard to potential "fairness and privacy" breaches by the broadcaster.
"Ofcom is investigating the fairness and privacy issues raised by Sky News' statement that it had accessed without prior authorisation private email accounts during the course of its news investigations," he said. "We will make the outcome known in due course."
Under Ofcom's broadcasting code, Rule 9.1 states that: "Any infringement of privacy in programmes, or in connection with obtaining material included in programmes, must be warranted."
It is expected that the regulator will report back in the Sky News investigation within 90 days.
Ryley is currently giving evidence to the Leveson Inquiry into press ethics and standards in London.
Intercepting emails is illegal under the Computer Misuse Act, and public interest is not technically a viable defence.
However, Ryley noted earlier in the month that the Crown Prosecution Service has said that it can sometimes be justified for a journalist to commit the offence where the story is in the public interest.
He pointed to the Daily Telegraph exposé of the MPs' expenses scandal, which came about after the paper paid for stolen data, while The Guardian has also admitted hacking a phone for a story.
The Metropolitan Police is also currently investigating instances of computer hacking and email interception as part of its Operation Tuleta probe.
Rupert Murdoch's The Times is also being sued over alleged email hacking for a story unmasking political blogger 'Nightjack'.