The monster vegetable tipped the scales at 17lbs 15 and a half ounces - breaking the previous world record of 16lbs 8.37 ounces held by John Sifford, of the West Midlands, since 2005.
World's biggest ever onion Photo
Peter, a 67-year-old retired chartered surveyor, who lives near Newark, has broken ten world records in his 30 years of gardening.
He has been trying for the honour of cultivating the world’s heaviest onion for 25 years but always missed out until yesterday’s victory at Harrogate Flower Show.
He then wrapped it carefully in towels - to avoid it being bruised by potholes - before loading it into his estate car for the overnight drive, arriving at the Great Yorkshire Showground about 4am.
There was then a nail-biting wait while dozens of rival entries were loaded onto the scales before Peter was announced as the winner.
As well as the winning weight, the onion was also found to measure 30ins in circumference and 24ins from top to bottom.
He said yesterday: 'It has taken me at least 25 years. I have been growing them for that length of time.
'In that time, I have been very close to the world record but it always escaped me. It is the same seed as last year.
'But I have invested more time and money into growing it including automatic venting and heating.'
He also concentrated on a batch of just 10 plants instead of his usual 50 to pick a winner.
He grew them in 150 litre plant pots - big enough for a large tree - in John Innes Number 3 soil. 'I have been talking to them for nearly 12 months,' he added.
'I always asked them if they wanted more water and food.” He currently holds three other world records - heaviest potato, heaviest parsnip, and longest beetroot.