Army of two

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Elite PMC (50 points): Complete all missions as a Professional.
My Virtual Friend (35 points): Complete all missions with the Partner AI.
Say Hello to my Little Friends (45 points): Purchase the MP7, M134, DAO-X Protecta, MGL MK-X, and the M107 Light Fifty.
Man of Many Masks (50 points): Purchase every mask variant.
If I Were a Rich Man (40 points): Earn one million dollars in total over the course of campaign mode.
Fear is The Mind Killer (45 points): Spend 1 minute straight at full Aggro.
Starting a Riot (30 points): Kill 50 enemies total in Co-op Riot Shield.
Two Eyes are Better Than One (35 points): Kill 5 enemies total using Co-op Snipe.
Seven-six-two Millimeter (20 points): Kill 250 enemies total using Assault Rifles.
This is my Boom Stick! (20 points): Kill 250 enemies total using Shotguns.
Spray and Pray (20 points): Kill 250 enemies total using Machine Guns.
Dead Man's Hand (20 points): Kill 150 enemies total using Handguns.
Alright, Who Wants Some? (20 points): Kill 250 enemies total using SMGs.
One Shot. One Kill. (20 points): Kill 100 enemies total using Sniper Rifles.
Big Boom! Big Bada Boom! (20 points): Kill 25 enemies total using RPGs.
Flip You. Flip You For Real (20 points): Kill 50 enemies total using the Melee Attack.
Fission Mailed (20 points): Kill 25 Martyrs by shooting the Bomb Packs on their chests.
If It Bleeds, We Can Kill It (30 points): Kill 25 Heavy Armor enemies.
Field Medic (30 points): Drag and heal your partner 25 times.
Boots on the Ground (10 points): Finish playing a versus ranked match.
The Devil's in the Details (20 points): Complete 20 minor objectives in a ranked match.
Surviving The Game (25 points): Complete a ranked match without ever needing to be revived.
Retirement Savings Plan (40 points): Earn one billion dollars in total in ranked matches.
Out of Debt (15 points): Heal your partner for the first time. Training does not count.
One Gun is Enough (35 points): Win a ranked match without purchasing any additional weapons.
Beast with Two Fronts (20 points): Kill 50 enemies total in Back-to-Back.
Running Man (30 points): Kill 75 enemies while in the stealth mode of Overkill.
L'Abattoir (30 points): Kill 100 enemies while in the power mode of Overkill.
Weapon Specialist (15 points): Purchase 3 weapons.
Stonewall (30 points): Kill 30 enemies using the Riot Shield melee attack
My Kind of Case! (40 points): Collect all of the information cases in the entire game.

Additionally, there are six secret achievements:

Mission 1 Complete (30 points): Completed Mission 1 as Contractor or higher.
Mission 2 Complete (30 points): Completed Mission 2 as Contractor or higher.
Mission 3 Complete (15 points): Completed Mission 3 as Contractor or higher.
Mission 4 Complete (15 points): Completed Mission 4 as Contractor or higher.
Mission 5 Complete (15 points): Completed Mission 5 as Contractor or higher.
Mission 6 Complete (15 points): Completed Mission 6 as Contractor or higher.

The following achievements require the Veteran Map Pack downloadable content and includes two secret achievements:

That's right. Who's laughing now (15 points): Buy the "Pack 8" gun pack in a multiplayer ranked match.
Arnold Braunschweiger (20 points): Destroy 300 destructible objects in Mission 7 and 8.
I promise to kill you last (30 points): Kill Dalton in less than 40 seconds.
I wanna be a cleaner (25 points): Final blow to Dalton is a headshot with a pimped .44 model 29 handgun.
Mission 7 Complete (30 points): Complete Mission 7 on the Professional difficulty.
Mission 8 Complete (30 points): Complete Mission 8 on the Professional difficulty.

The following achievements require the SSC Challenge Map Pack downloadable content:

True SSC Challenger (25 points): Win every stage of a ranked three round SSC Challenge match.
Barrel SSC Challenger (25 points): Destroy 500 barrels in ranked SSC Challenge matches.
SSC Challenge Win (25 points): Win a ranked SSC Challenge match.
SSC Challenge Marksman (25 points): Achieve 75% accuracy at the conclusion of a ranked three round SSC Challenge match.