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