The 5.5% hike on standard variable tariffs (SVTs) will come into effect from 1st June, adding £63 to a typical annual dual fuel bill.
The Big Six supplier said the price rise follows rising wholesale energy costs and mandatory non-energy costs, such as delivering low carbon electricity and upgrading meters.
It expects the number of people on SVTs to continue to reduce this year as it no longer moves customers to the more expensive tariffs automatically at the end of a fixed-term contract.
Neil Clitheroe, CEO of Retail at ScottishPower said: “Unfortunately, our standard variable prices are increasing. This reflects rising wholesale energy costs and compulsory non-energy costs. Two-thirds of our customers are unaffected.
“We will be contacting all customers affected by the price change to give them the opportunity to move to a fixed price tariff alternative and avoid this increase.”