Adams has won four world titles and two Olympic golds but Walsh's medal was the first of any hue for a New Zealand man at the worlds, coming a year after he won Olympic bronze in Rio.
Walsh was already guaranteed gold on Sunday thanks to his third-round put of 21.75 metres but finished with a flourish by hurling the weight 22.03m on his final attempt.
All six efforts were well over 21 metres in a remarkable display of consistency.
He did have a scare, though, when American Joe Kovacs thought he had snatched victory to retain his title with his last attempt which was measured at 22.08 metres.
It was ruled as a foul, however, with Kovacs adjudged to have put his foot on the top of the throwing circle perimeter.
The U.S. team appealed against the decision but it was overturned.
Kovacs took silver with his third attempt of 21.66m and bronze went to Stipe Zunic of Croatia with 21.46. It was the first senior medal for the 26-year-old, who celebrated by rolling on the infield of the London Stadium.
"It was a hell of a competition out there. It's awesome. It's something I've always dreamed about, being a world champion," Walsh said.
Zunic's bronze medal was all the more impressive as it came only three years after he took up the event.
"I did javelin before, I was ready for London 2012 as a javelin thrower but I suffered from a shoulder injury so I could not continue," he said.
"This is amazing when I am among these big guys. I was 13th coming to this competition but I managed to handle this pressure well."
(Editing by Ed Osmond)
