Representatives from Highland Council along with Scottish economy secretary Keith Brown and UK minister Andrew Dunlop attended the event.
Announced in March last year, the deal involves direct funding and greater borrowing powers.
There has been criticism that the funding package will not benefit the wider Highland area.
The signing ceremony in Invergordon included an agreement to release £12.25m of funding on three projects.
These are the Science Skills Academy STEMD, which is a a network of "science rooms" to promote learning in science and engineering, and the University of the Highlands and Islands' School of Health, Social Care and Life Sciences.
Also, a land remediation project which aims to make vacant land at Inverness' Longman available to businesses.
Other spending planned at a later date includes about £15m to turn Inverness Castle from a criminal and civil courts building into a tourist attraction.
The £315m Inverness City Region Deal has been formally signed off in a ceremony in Invergordon.