As defence correspondent of the Daily Express he beat his rivals to a string of scoops.
One of his great strengths was the ability to remember minute details without having to make a single note.
After his retirement he published a series of books alleging Britain's security services had been penetrated by spies at the top level.
Harry Chapman Pincher, son of an Army officer, was born in India on 29 March 1914.
He went to Darlington Grammar School and London University, and graduated  in zoology and botany.
Ironically while at university, some fellow students tried to sign him up to the Soviet cause.
"I said to one: 'In the event of a successful revolution, how would the new England be governed?'
"He said: 'To start with it would be governed from Moscow.'
"So I said: 'Well, bugger that.'"
Pincher worked as a teacher before joining the Royal Armoured Corps in 1940. He moved to the Rocket Division of the Ministry of Supply in 1943.
After the war he secured a job with the Daily Express as defence, science and medical editor.
One of his best contacts, the chief scientist at the Ministry of Defence in the 1950s, was keen to tell him as much as possible about Britain's atomic weapons programme.
He wanted to explain to the public why the country was spending such massive sums of money on it.
"I'm up for use any time," he said. "If someone wants to come and tell me some news that nobody else knows and I make a lovely scoop of it, come on, use me!"
But it never worried him that he was being used by senior figures with ideas to promote or scores to settle.
His investigative methods were unorthodox. Mainly he bought people agreeable lunches and, over the claret, senior civil servants and politicians would tell him things.
His favourite lunch venue was a classy French restaurant called L'Ecu de France in Jermyn Street off Piccadilly, handy both for Fleet Street and for the civil servants and politicians in Westminster.
Only after it closed did he learn that the place had been bugged by MI5 since the 1940s. (It had also, MI5 discovered when removing its own hidden microphones, been bugged by the KGB.)
"MI5 heard every conversation that I had and they did nothing about it," he said.
"All they did was put it in the files. MI5 doesn't like to take any action; they like to know.
"'It's in the files: if we take action, they'll know we know.' That's the attitude. It's absolutely crazy."
Pincher cultivated contacts not only at the lunch table but in the countryside.
In the 1950s he took up game shooting, and met a good many useful sources while banging away in plus-fours at pheasant and grouse.
Lord Mountbatten, aloof and unapproachable as first sea lord and chief of the defence staff, turned out to be much friendlier when Pincher encountered him shooting.
"He invited me to shoot at Broadlands and even dictated a story to me once when I was travelling in his Land Rover, which went straight into the newspaper... but under my name, not his."
In 1964 he brought into the open the scandal over Ferranti's Â£5 million profit on Bloodhound missiles, which were the major weapon in Britain's air defences.
This was a colossal sum at the time and a subsequent inquiry saw the company refunding more than Â£4 million to the Treasury.
In 1971, Pincher revealed how the number of staff at the Soviet embassy had increased significantly and claimed that most of the diplomats, chauffeurs and gardeners were really spies.
This prompted Edward Heath's government to expel 105 of them, which seriously damaged the Soviet Union's espionage capability.
After his retirement, Pincher's most controversial book was Their Trade is Treachery. This revealed the head of MI5 until 1965, Sir Roger Hollis, had been investigated as a suspected Soviet spy.
There was an immense furore, which Pincher doubtless found most gratifying.
In the years since, Pincher hardened his line on Hollis, and continued researching the subject becoming convinced that Hollis actually was a Soviet mole.
Not everyone agrees. Christopher Andrew, MI5's official historian, thinks it's nonsense to suggest Hollis was a traitor.
Rupert Allason, who writes about espionage under the pen name Nigel West, is more nuanced. "Some people don't believe there was any hostile penetration of the security service.
"Personally I've seen the evidence: I know there was penetration up until at least September 1963.
"Where I part company with Harry is on the issue of candidates. He believes it was Sir Roger Hollis, I'm not convinced of that; but I am persuaded there was a mole."
One of the main sources for Pincher's book was the former MI5 agent Peter Wright, whose book Spycatcher was the subject of a long court case to try to prevent publication.
Margaret Thatcher's government was infuriated by Their Trade is Treachery; but then angering prime ministers was nothing new to Pincher.
In May 1959, Conservative Prime Minister Harold Macmillan wrote a personal minute, marked "secret", to his minister of defence.
"I do not understand," he wrote, "how the Express alone of all the newspapers has got the exact decision that we reached at the cabinet last Thursday on space. Can nothing be done to suppress or get rid of Mr Chapman Pincher?
"I am getting very concerned about how well informed he always seems to be on defence matters."
And the Labour Prime Minister Harold Wilson contributed to what may have been Pincher's finest moment in 1967.
What became known as "the D notice affair" began with a "walk-in", a member of the public who turns up at a newspaper's front door with a possible scoop.
The information given to Pincher was that all private cables and Post Office telegrams were being intercepted and that some were being read by GCHQ.
Before publishing the story, Pincher checked with a contact called Lt Col Sammy Lohan, secretary of the D notice committee.
The D notice system is a voluntary one, designed to alert the news media to stories that might damage national security if published.
Lohan told Pincher his story was not covered by any D notices, and the Express went ahead and printed the scoop.
Wilson was furious and set up an inquiry to show that D notices had in fact been breached. The inquiry concluded the exact opposite, and vindicated the Express.
In his Who's Who entry, Pincher listed ferreting in Whitehall and bolting politicians as two of his recreations.
He said he didn't regret a single thing he had found out and printed.
"I always tried to meet all the top people because that's where the stories lay," he said.
"When you have access to people you have access to facts, usually secret facts."
Chapman Pincher was known as "the lone wolf of Fleet Street".