Around 435,000 people are paid less than the living wage in Scotland, an increase of more than 70,000 from an estimated 360,000 in 2012, KPMG said.
The wage is a benchmark based on the amount an individual needs to earn to cover the basic costs of living. It is set at £8.55 an hour in London and £7.45 an hour in the rest of the UK and is voluntary for employers.
Supporters believe it will boost living conditions if adopted by employers.
In April, the Scottish Government implemented a Scottish living wage of £7.45 for public sector workers and encouraged private sector employers to follow guidelines set out by the Scottish Living Wage Campaign.
Labour leader Ed Miliband said if his party wins the next General Election, it will offer firms a 12-month tax break in 2016 if they pay the living wage.
The proportion of Scottish workers paid below the figure is 20%, slightly below the rest of the UK where 21% of employees are paid less than the living wage, according to the KPMG research.
In Scotland, the areas with highest proportion of workers paid below the living wage are Dumfries and Galloway at 36%, Clackmannanshire at 29% and East Renfrewshire at 20%.