The 40m x 10m banner overlooks George Square and its bars, clubs, restaurants, shops, banks and offices in the centre of Glasgow. Forrest claims the site will reach more than 40,000 people a day.
The contract for the banner was awarded by the managing agent DTZ after a competitive pitch. Large-format outdoor media owner Blow Up is understood to have been involved in the process.
Fellow outdoor media owner Ocean Outdoor used to sell a site on George Square, but no longer does so and this is a completely new contract.
Marc Keenan, managing director, Forrest Media, said: "George Square was a very important win for us and gives us the ability to offer advertisers the perfect strike, right in the heart of the city of Glasgow"
Forrest has also expanded its site at Haymarket in Edinburgh. The site used to be made up of three 96-sheets and one 48-sheet, but they have been redeveloped and replaced with four 96-sheets.
The development means advertisers can use all four sites for a single creative.
Keenan said: "Haymarket is THE location in Edinburgh – a no brainer as far as I can see, for our clients to achieve massive stand-out in a very important city centre."
Forrest Media sells advertising on backlights, giant banners and city screens in Scotland and England.