News of the deal comes only a week after the Scottish firm revealed its new name and identity under the Forrest group of companies led by Chris Trainer.
It presents an opportunity to develop the market for large-scale poster sites north of the border.
Giant posters are fast becoming an accepted part of outdoor media, particularly on scaffolding used on building and renovation work.
Forrest Group chief executive Chris Trainer said: "This is a terrific deal for us as it gives us the ability to offer advertising agencies and media buyers access to different and much larger sites.
"We'll be looking to develop sites across Scotland and I know that property developers will see the benefits a Mega Forrest banner can bring."
Mega Profile is one of the UK's leading giant poster providers. Its list of advertisers includes American Airlines, Renault and the Harry Potter films.
In 2000 it secured the rights to mount advertising on the side of Fort Dunlop on the M6, which has been recognised by the Guinness Book of Records as the world's largest billboard.
Mega Profile chief executive Simon Evans said: "We are very pleased to be joining forces with Forrest Outdoor Media.
"They can access some quality sites and I'm certain both our companies will benefit from the merger."
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