Here is the full list of all 48 DiRT 4 achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Complete back to back Weekly Community Events
Destroy 100 blocks in 60 seconds in Joyride
Hire a fourth Engineer onto your Team
Complete all 12 Stages of a Monthly Event in Community Events
Finish three sectors of a Stage with a flat tyre
Upgrade three Facilities to Grade A quality
Triumph in the face of adversity
Finish in the Top Tier of a Delta Daily in Community Events
Finish in the Second Tier or higher in a Daily in Community Events
Finish a Stage in sunny conditions in Community Events
Win a Stage at night
Earn the International Off-Road C-3 licence
Earn the International Rally H-C licence
Qualify for an A-Final in a Landrush Event in Career
Earn the International Rally R-3 licence
Earn the National Stadium Pro-3 licence
Get an overall win in the lowest eligible Vehicle Class in a Rally Event in Career
Win your class in a multi-class Event in Career
Buy a vehicle from the Classifieds
Earn the Fearless Bonus in a Stage or race
Call in the Chief Engineer's recommendations during a Service Interval
Finish in first place in a Career Event
Win a Stage in Headcam
Complete a clean Stage or race
Complete all of the Advanced Driving Techniques at the DiRT Academy
Complete the Welcome Event
Cleanly land a jump longer than 65m
Earn the International Rally R-1 licence
Earn the International Rally H-A licence
Earn the National Stadium Pro-1 licence
Earn the International Off-Road C-1 licence
Qualify in the top spot in a Rallycross Event in Career
Win the Global Rally Series
Win the FIA World Rallycross Championship
Win the Landrush World Series
Win the Historic Legends Series
Win the Triple Crown
Own a vehicle equipped with all Grade A parts
Complete a Stage or race with the Fearless Preset active
Get a bad case of the Mondays
Set a time in every challenge in a single Joyride Chapter
Achieve 10 Gold medals in Joyride
Set a Gold medal time in a Time Attack challenge without hitting a penalty marker
Complete an Event in Jam Session
Get promoted to a new Tier in Pro Tour
Complete 25 Events in Pro Tour
Take two Joker Laps and win a Rallycross race
Repair your car on Stage and win the Stage