Full list of all 69 Borderlands 2 achievements worth 1,625 gamerscore. It takes around 40-50 hours to unlock all of the achievements in the base game.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 4 DLC packs containing 19 achievements worth 625 Gamerscore.
Completed all side missions
Defeated Terramorphous the Invincible
Completed level 1 of all non-level-specific challenges with a single character
Gunzerked continuously for 90 seconds
Remained in Zero's Deception mode for ten seconds straight
Killed Donkey Mong
Discovered all named locations
Reached level 50
Discovered all named locations in Three Horns, Tundra Express, and Frostburn Canyon
Discovered all named locations in Eridium Blight, Arid Nexus, and Sawtooth Cauldron
Had Purple-rated gear or better equipped in every slot
Discovered all named locations in The Highlands, Thousand Cuts, and Wildlife Exploitation Preserve
Allowed a Goliath to level up four times before killing him
Killed a Chubby
Defeated Jack
Completed the mission "Data Mining"
Opened the chest at the bus stop in Fyrestone
Completed the mission "Toil And Trouble"
I can't even capture it on my camera
Completed the mission "Where Angels Fear To Tread"
Completed the mission "The Man Who Would Be Jack"
Discovered all named locations in Sanctuary, Opportunity, and Lynchwood
Completed Round 5 of any Circle of Slaughter
Completed the mission "The Once and Future Slab"
Reached level 25
Completed the mission "Shoot This Guy in the Face"
Completed the mission "Wildlife Preservation"
Completed the mission "Bright Lights, Flying City"
Completed the mission "Rising Action"
Completed the mission "A Train To Catch"
Killed a Constructor without it ever building another bot
Tipped Moxxi $10,000
Phaselocked 100 enemies
Killed 100 enemies with the Sabre turret
Completed the mission "A Dam Fine Rescue"
Completed 20 side missions
Purchased 5 items from the black market
Killed a flying enemy with a thrown Tediore weapon
Redeemed 25 tokens
Gave Claptrap a high five
Got an item from Michael Mamaril
Completed the mission "Hunting The Firehawk"
Reached level 10
Completed the mission "Plan B"
Completed the mission "The Road To Sanctuary"
Completed the mission "Best Minion Ever"
Reached level 5
Revived someone from "Fight for Your Life!" that is on your friends list
Unlocked 10 customization items
Completed the mission "My First Gun"
Completed all Pirate's Booty side missions
Discovered all named locations in Oasis and the surrounding Pirate's Booty zones
Completed the mission "X Marks the Spot"
Collected 10 pictures of Moxxi in Campaign of Carnage
Completed all Campaign of Carnage side missions
Completed the mission "Long Way To The Top"
Completed all Hammerlock's Hunt side missions
Discovered all named locations in Hammerlock's Hunt
Completed the mission "The Fall of Nakayama"
Vanquished the Ancient Dragons of Destruction
Won the most challenging round in Murderlin's Temple
Fed thy noble queen 3 times during one visit to her quarters
Wielded the Mysterious Amulet
Completed thy quest by rescuing yonder queen
Demonstrated your skill, or lack thereof, at rolling the magical treasure orb of many sides
Showed thine worst enemy, the abomination known as "The Darkness," who is the nerdiest of them all
Unsheathed 5 swords from Immortal Skeletaurs without leaving the area
Introduced thyself to the White Knight
Slew Mister Boney Pants Guy