Achieve first place finishes in all DiRT Tour events

This is where most of your time will go in getting this platinum. There are 4 seasons with 4 events in each that you need to complete. You need to win every race in all of them, the DC challenges aren't necessary for this particular trophy but are needed for "Platinum Performance" and, as a result, the platinum. There are also the 6 world tour events for each of the specific disciplines. Win all these events in to this trophy. The difficulty can be set to 1 the entire time if you want an easy ride. For reference, you need to win all the races in the following events:

Season 1:
Alpine Stars Trophy
Transworld Clash
Brembo Blast
Gymkhana Academy

Season 2:
Rampage
Pro Invitational
Offroad Rush
X Games

Season 3:
International Skirmish
Gold Series
Shoot Out
Winter X Games

Season 4:
Masters Championship
All Stars Show Down
Global Legends
SuperSeries

World Tours:
Rally World Tour
Rally Cross World Tour
Trailblazer World Tour
Land Rush World Tour
Head 2 Head World Tour
Gymkhana World Tour