The YouGov poll found 90 per cent of respondents believe promotions such as buy one get one free - known as Bogofs - are influential in getting people to buy unhealthy snacks.
More than a fifth of four and five-year-old children in Scotland are overweight or obese - making them five times more likely to be obese as an adult.
Cancer Research UK is calling on the Scottish Government to introduce legislation which restricts junk food price promotions.
Linda Bauld, a professor at the University of Edinburgh, said: “Sadly Scotland’s weight problem is becoming ever obvious and it’s clear from this survey that the public recognise the damaging impact of price promotions.
“The Scottish Government has a role to play to help us all eat a better diet. The introduction without delay of world-leading laws to prevent price promotions from continuing to fuel Scotland’s obesity epidemic would be an important step towards turning the tide on a crisis that’s damaging the health of so many people across Scotland.”
Excess weight is Scotland’s biggest preventable cause of cancer after smoking, with around 2,200 cases a year attributed to being overweight or obese.
Around six in ten parents said they backed plans for the Scottish Government to restrict price promotions on foods high in fat, sugar and salt.
The survey - of 1,037 adults in Scotland - also revealed 77 per cent of Scots parents agreed that the price of unhealthy food was contributing towards people being overweight and obese.
Besides Bogofs, 88 per cent said price deals that reduced the cost of junk food - for example 50 per cent off - influenced what people bought.
Steve Turner, of the Royal College of Paediatrics and Child Health at the University of Aberdeen, said: “Childhood obesity causes health problems for children. Obesity often continues from childhood into adulthood and adult obesity is a major preventable risk factor for cancer and is associated with a wide range of illnesses and premature death.
“With far too many of our children carrying too much weight today, there’s no time to waste as we try to prevent ill health in today’s children and tomorrow’s adults.
“In Scotland, too much sugary food and drink is purchased on price promotion. The tide must be turned on this. The future health of Scotland’s children depends on it.”