Each class has distinct proficiencies in three main areas: general combat using firearms or melee strikes, tech attacks, and biotics. Each class has a unique pool of available abilities plus a corresponding unique class ability that improves attributes important to that class.
In the original Mass Effect, abilities are referred to as talents, whereas in Mass Effect 2 and Mass Effect 3 they are referred to as powers. In all three games abilities can be upgraded through the allocation of points that are gained from leveling the character. Newly-created or imported characters begin the game with points already allocated in certain abilities by default; these vary by class.
Classes have unique attributes and can be further specialized to have even more intense focuses or proficiencies:
Mass Effect
The Adept and the Vanguard can't increase their First Aid healing with their own talent points and must rely on squad members to gain greater healing from medi-gel (or pick First Aid as a bonus talent).
The Soldier possesses neither Electronics or Decryption in its default talent pool and must either pick one of said talents as a bonus option if feasible and/or rely on the squad for the expertise to access secured gameworld objects.
The Soldier regenerates a small amount of health over time by default.
There are six specializations, two of which are available based on your initial class choice.
Selecting a specialization offers access to a new trait that add ranks 7-12 to your class specific talent; ranks 1-6 are unchanged, and grant the same bonus when you take ranks 7-12. Specializations are only unlocked once per player character and will then carry over to subsequent playthroughs with that character.
Specializations are not available for NPC squad members.
Mass Effect 2
Unlike in the first game, each class has a unique active power not available to the others that provides special advantages in combat.
Each class possesses a unique passive power that can be further specialized in one of two ways at maximum rank (rank 4).
The Soldier has a slightly higher amount of base health than the other classes and can storm (sprint) faster. It also gains a time dilation effect while storming in combat. It is the only class whose class power, Combat Mastery, does not increase power recharge speed.
The Infiltrator's class power grants it a time dilation effect while zoomed through the scope of a sniper rifle.
The Engineer's class power Tech Mastery can lower the cost of Research projects in the Normandy Tech Lab.
The Sentinel's Tech Armor has the unique ability to instantly recharge squadmate powers when activated (Tech Armor ranks 3 and 4 only).
Mass Effect 3
Each class has two unique active powers not available to the others that provide special advantages in combat.
The class passive works much like it does in Mass Effect 2, only now ranks 4-6 all have two different options for specialization, as do ranks 4-6 on all other available powers.
There is no unique "title" or named identity for any of the specializations like there is in the previous two games.
The Infiltrator's class power grants it a time dilation effect while zoomed through the scope of a sniper rifle (single-player only).
The melee-oriented evolutions of the Fitness passive power have unique class-specific effects.
The damage of heavy melee attacks is greatly boosted by the Rank 6 Tech Vulnerability evolution of Sabotage for the tech-oriented classes (Engineer, Sentinel, and Infiltrator) in single-player and also for several classes in multiplayer. The heavy melees of most of the classes also have some other unique attributes in either game mode.
Class Equipment
Class also influences what weapons a character is proficient with and also what other armors and equipment it may use:
Mass Effect
The more combat-oriented classes (Soldier, Vanguard, Infiltrator) can wear heavier types of armor (medium and heavy) and therefore have better resistance against sources of damage that can bypass shields.
Classes less proficient in general combat may not even have the option to train with a particular weapon type and cannot aim as effectively with those weapons (e.g. the Engineer cannot zoom through the scope of sniper rifles). Some of these restrictions are eased in Legendary Edition.
Certain classes are able to equip advanced omni-tools or biotic amps that can provide substantial bonuses to power recharge speeds, First Aid cooldown, and shield strength.
Mass Effect 2
Class can determine if a particular category of weapon (e.g. shotguns) can even be equipped at all.
The more combat-oriented classes gain special weapon upgrade options not available to the other classes about halfway through the story.
Mass Effect 3
Weapons and some equipment have weight attributes that can impact how often powers can be used. The more combat-oriented classes can generally carry heavier gear without penalty compared to the more tech/biotic power-oriented classes.
Mass Effect: Andromeda no longer uses the class system, and any Ryder is able to learn any skill. However, they are attached to training groups and focusing on a training group provides access to a class-like mechanic known as a Profile. Of the seven Profiles, six of them roughly correspond to the traditional trilogy classes, and one is unique to the game.
Trivia
According to gameplay statistics for Mass Effect Legendary Edition as of July 27, 2021, 40% of players are Soldiers, followed by 21% Vanguards, 15% Infiltrators, 11% Adepts, 8% Sentinels, and only 5% Engineers.[1]