The new company becomes the world's biggest standalone consumer health business, home to brands including Sensodyne toothpaste and Advil painkillers.
Haleon shares will trade under the ticker 'HLN' on the London Stock Exchange.
GSK, meanwhile, will become New GSK, focused solely on vaccines and prescription drugs.
The new business has been buoyed by recent clinical trial successes, including its potential blockbuster RSV vaccine, and a cash boost from the consumer health spin-off.
With the split complete, all GSK shareholders receive one Haleon share for each GSK share they own.
On Monday, GSK shares will trade excluding the value of the consumer healthcare business, so its price will likely drop.
After close of trading on Monday, GSK will consolidate its share price, returning it to roughly the same as before the demerger.
That will ensure the company's earnings per share and share price can be confirmed with previous periods, it has said.
The ratio for the GSK share consolidation will depend on fluctuations in the volume and price of GSK shares during trading on Monday, the company said.
In a statement on its website, GSK said, 'GSK plc as today (Monday 18 July 2022) completed the demerger of the Consumer Healthcare business from the GSK Group to form the Haleon Group. The shares of Haleon plc will be admitted at 8.00 a.m. today to the Premium Listing segment of the Official List and to trading on the Main Market of the London Stock Exchange'.
— Haleon (@Haleon_health) July 18, 2022