Here is the full list of all 48 DiRT 4 achievements worth 1,000 gamerscore. It takes around 60-80 hours to unlock all of the achievements on Xbox One.
Won the Historic Legends Series
Earned the International Rally H-A licence
Completed a Stage or race with the Fearless Preset active
Achieved 10 Gold medals in Joyride
Destroyed 100 blocks in 60 seconds in Joyride
Won the Triple Crown
...it's gonna be a long week
Repaired your car on Stage and won the Stage
Won the FIA World Rallycross Championship
Qualified in the top spot of a Rallycross Event in Career
Took two Joker Laps and won a Rallycross race
Won the Global Rally Series
Set a Gold medal time in a Time Attack challenge without hitting a penalty marker
Cleanly landed a jump longer than 65m
Completed 25 Events in Pro Tour
Got promoted to a new Tier in Pro Tour
Finished three sectors of a Stage with a flat tyre
Earned the International Rally R-1 licence
Won a Stage at night
Completed all of the Advanced Driving Techniques at the DiRT Academy
Completed an Event in Jam Session
Earned the International Off-Road C-1 licence
Owned a vehicle equipped with all Grade A parts
Upgraded three Facilities to Grade A quality
Hired a fourth Engineer onto your Team
Earned the International Off-Road C-3 licence
Set a time in every challenge in a single Joyride Chapter
Won the Landrush World Series
Bought a vehicle from the Classifieds
Earned the International Rally H-C licence
Earned the National Stadium Pro-1 licence
Completed all 12 Stages of a Monthly Event in Community Events
Completed back to back Weekly Community Events
Triumphed in the face of adversity
Qualified for an A-Final in a Landrush Event in Career
Earned the International Rally R-3 licence
Earned the National Stadium Pro-3 licence
Got an overall win in the lowest eligible Vehicle Class in a Rally Event in Career
Won your class in a multi-class Event in Career
Finished in first place in a Career Event
Won a Stage in Headcam
Earned the Fearless Bonus in a Stage or race
Called in the Chief Engineer's recommendations during a Service Interval
Finished in the Second Tier or higher of a Daily in Community Events
Finished in the Top Tier of a Delta Daily in Community Events
Finished a Stage in sunny conditions in Community Events
Completed the Welcome Event
Completed a clean Stage or race