In an eagerly awaited appearance before the U.K.'s media ethics committee, Morgan, who replaced Larry King on CNN, was visibly tense, sometimes hostile and often rejected characterizations of his actions made by inquiry lawyers as "nonsense."
The stakes were high for Morgan. More than a dozen journalists have been arrested, senior executives with Rupert Murdoch's News Corp. media empire have lost their jobs, and top U.K. police officers have resigned over their failure to tackle the phone hacking scandal. His testimony Tuesday was given under oath, and Morgan could be subject to criminal proceedings if he was found to have violated any British laws.
Before his U.S. television career, Morgan ran two British tabloids -- first Murdoch's News of the World and then the Daily Mirror, owned by Murdoch competitor Trinity Mirror.
A key line of questioning centered on comments Morgan made in a 2006 article in the Daily Mail tabloid. In it, Morgan said he was played a phone message left by the former Beatle on Mills' answering machine, describing it in detail and noting that McCartney "even sang 'We Can Work It Out' into the answerphone."
Mills, who went on to divorce McCartney in one of most expensive separations in British history, has said there's no way Morgan could have obtained the message honestly.
Morgan on Tuesday stubbornly refused to answer almost any questions about how he came to hear the message, saying: "I'm not going to start any trail that leads to the identification of a source."
But when asked by inquiry chief Lord Justice Brian Leveson whether he could supply any information to back the assertion that he had heard the recording legally, the 46-year-old journalist said he couldn't.
Earlier, Morgan said he "doesn't believe" he had ever listened to hacked voicemail messages -- and dismissed earlier interviews in which he'd discussed phone hacking at length as having been based on rumor and hearsay.
He also refused to say who had filled him in about the practice.
"My memory's not great about this. It was a long time ago," he said.
Morgan was giving evidence to Britain's media ethics inquiry by video link Tuesday from the United States -- one of dozens of phone hacking victims, journalists and tabloid executives to face the inquiry, set up in the wake of the uproar over phone hacking and other unethical newsgathering methods at the News of the World.
The atmosphere turned tense within minutes of Morgan taking his oath. He was quizzed about his relationship to private investigators and freelancers such as "Benji the Binman," who specialized in raking though celebrities' trash to look for scoops.
Morgan said he never dealt with private investigators but he did acknowledge buying information from Benji -- and said he'd had some qualms about it.
"Did I think he was doing anything illegal? No. Did I think he was doing anything on the cusp of unethical? Yes," Morgan said.
Witnesses at the inquiry have exposed the seamy side of British journalism, with reporters accused of cooking up stories, blackmailing subjects, hacking phones and paying bribes to police officers to secure tips.
Murdoch himself may testify before the inquiry, according to an offhand comment made by inquiry lawyer Robert Jay. At one point Jay told Morgan to stop speculating about what Murdoch might have remembered about a particular incident in which the two of them clashed.
"We can ask him for his recollection of events when we get there," Jay said.
The inquiry declined to comment further, and News Corp. did not immediately return an email seeking confirmation. Murdoch earlier in the year testified before Parliament on the subject of phone hacking and shut down the 168-year-old News of the World in July after the full hacking scandal broke.
CNN, meanwhile, broadcast its star's testimony live Tuesday, but only to its international subscribers.
Separately, Murdoch's News Corp. media empire announced settlements with seven more prominent figures in the wake of the phone hacking scandal at the News of the World.
The company said in a statement Tuesday it had settled claims brought by Princess Diana's former lover James Hewitt, ex-Liberal Democrat lawmaker Mark Oaten, TV presenter Ukrika Jonsson, model Abi Titmuss and Paul Dadge, who helped rescue victims of the 2005 London transit bombings. Theatrical agent Michelle Milburn and Calum Best, the son of soccer legend George Best, rounded out the settlement list.
At least one more settlement -- with former England soccer player Paul Gascoigne -- appeared imminent, according to lawyer Jeremy Reed.
The terms of the new payments announced Tuesday were not disclosed but they are likely to be substantial.
Actress Sienna Miller earlier received 100,000 pounds (nearly $157,000) in damages when she settled with News International; the family of murdered British schoolgirl Milly Dowler were awarded 2 million pounds ($3.1 million) plus 1 million pounds ($1.6 million) from Murdoch himself, which was earmarked for charity.