After progressing enough in the Campaign, you will be given the opportunity to participate in Championships, which function just like Horizon 2. The new thing here is that you can also create Championship Blueprints.
To unlock this achievement, you need to drive up to a Route that enables you to start a championship from and create a new Blueprint. You must add 10 events. Make sure that two of them are circuit events and make them be around 15 laps. For the sake of saving time, let the other 8 be sprint events.
Once you've selected those, back out to the screen that all available Blueprints for that Route are. You'll be able to see your Blueprint's poster, on the bottom of which are the number of events (that should obviously be 10) and the total miles that you'll run for that Championship. You need to make sure that's 100 miles or more for the Imperial and 161 kilometers or more for the Metric system.
If those two number are ok, complete the Championship and the achievement will pop. You don't have to win it too to get it.