The latest national GP worklife survey, carried out by the University of Manchester, found that 39% of GPs planned to quit in the next five years - double the proportion who planned to do so in 2005.
GP leaders called the findings 'incredibly worrying', and warned that general practice was struggling under intense pressure.
The findings are a further dent in the government's target to increase the GP workforce by 5,000 full-time equivalent GPs by 2020/21, after a 4% drop in the workforce over the past two years.
One in five GPs said they work more than 60 hours a week, and 92.3% said they faced high or considerable pressure from increasing workloads - while 85.3% reported high or considerable pressure from having 'insufficient time to do justice to the job'.
Across more than 6,000 GPs who responded, the proportion planning to quit within five years was up from 35% in 2015. Among GPs over 50 years old, 62% now plan to quit inside five years, up from 61% two years earlier.
A total of 13% of GP aged under 50 reported a high or considerable likelihood they would leave direct patient care within five years, and just 45% said there was no likelihood of this.
Satisfaction with pay, working hours and responsibility, were slightly higher than in 2015, the report found, but scores remain lower than in surveys carried out before the new GP contract took effect in 2004.
Professor Kath Checkland, who led the study said: 'Although the declines in satisfaction seen between previous years has stopped, low satisfaction and high pressures have been sustained.
'The all-time high figure of 39% of GPs who say they intend to quit within five years is particularly worrying in terms of the possible implications it might have on recruitment, retention and patient care.'
RCGP chair Professor Helen Stokes-Lampard said: 'It’s incredibly worrying to hear that so many GPs are thinking about leaving the profession within the next five years, but it certainly isn’t surprising, given the intense pressures family doctors are facing.
'Pressures in general practice have reached an all-time high; our workload has escalated by at least 16% over the last seven years, but the share of the NHS budget general practice receives is less than it was a decade ago, GP numbers are actually falling, and many hard-working GPs are simply burnt-out and exhausted.
'As this study shows, 20% of GPs are now working intensively for more than 60 hours a week. We’re trying to do more and more on less and less, and there is a limit beyond which we can no longer guarantee that we are practising safely.'
GPC chair Dr Richard Vautrey said the findings were further evidence of the 'acute workforce crisis in general practice'. He said: 'As more GPs decide to leave the profession it will be patients who suffer. We know that they face unacceptably long waits for appointments, and this will only get worse as the number of GPs practising in surgeries across the country falls.'
A DHSC spokesman said: 'GPs are a vital part of the NHS and we recognise the everyday pressures they face – that’s why we’re increasing investment by £2.4bn a year by 2021 and recruiting 5,000 new doctors into general practice. '