The Evac app will provide visitors and residents with information in the event of a fire, flood or terrorist attack.
It has been launched ahead of the UEFA Champions League Finals which will see up to 170,000 football fans travel to the capital.
Cardiff council said the app was potentially a "life-saver".
The app provides push notifications to inform people of major incidents in the city, and if necessary, directs them to the nearest evacuation point.
There are also links to first aid videos and advice on what to do in the event of an attack.
Emergency Management Officer, Gwilym Owen, said: "It's highly unlikely that any of us will ever be caught up in a major incident, but if the worst happens, being informed and prepared can significantly reduce the risk of harm to people and property."
The app was developed over the last six months by Cardiff council in partnership with emergency services, health and transport bodies and counter terrorism teams.
A smartphone app to keep people in Cardiff safe in the event of a "major incident" has been launched ahead of the Champions League Finals.