It does not seem too possible to complete any of the Fallout games without killing at least some intelligent, living creatures. However, given the important role of combat in these games, it is surprising how close one can come to doing this in all the games.
In Fallout and Fallout 2, the two exceptions occur very late in the game and involve the elimination of the central villains. Bizarrely, in Fallout 3, of the three exceptions, one occurs during a tutorial quest, and the other two occur in the middle; none of these involve the death of named villains. In addition, many of the sub-quests that are not required to complete the game can also be completed without killing an enemy. Some of these offer substantial amounts of experience, so that this approach can be valuable for weak, low-level characters to level up.
Fallout can be completed without killing any characters in combat. However, to complete the game, it is necessary to use the computers on the lowest level of the Mariposa Military Base to destroy it and to detonate the atomic bomb beneath the Cathedral.
A character will be taken directly to the lowest level of the military base from Necropolis after talking with and surrendering to the supermutants. Alternatively, the base can be found by exploring the eastern edge of the map or from information in the Cathedral. Once captured, the character can escape from captivity by running away and hiding, then proceed to the control room, use the computer there to activate the self-destruct code, and then using stealth and fleeing to escape from the base before it explodes. Although there is an option to activate an alarm, it seems that the NPCs in the base do not respond to this and are destroyed when the base is destroyed.
The character can find the cathedral by talking with various NPCs. It is easy to get through the top floor of the Cathedral by simply walking through most of it and asking for permission to speak with Morpheus, it is then possible to sneak through the lower level to the entrance of the vault and to continue from there without hiding by using the robes from the Children's hospital in the hub. Near the elevator to the lowest level, there's a locker with a stealth boy, which can be used to remain hidden while approaching and activating the atomic bomb in the lowest level. (It is also, apparently, possible to persuade the master to destroy himself.) Since the master will detonate the bomb when defeated in combat or persuaded to destroy himself, there seems no way to prevent the detonation of this bomb.
Fallout 2 can be completed without killing any more than two characters: president Dick Richardson and agent Frank Horrigan. Richardson can be slain by planting explosives on him when picking his pocket. It seems necessary to kill Horrigan in combat, but this can be done easily since he will instantly die if injected with the poison from Doc Jubilee's house.
It was not entirely clear that Richardson needed to be slain. If he is slain, it is possible to set the turrets in the courtyard to counter insurgency mode. When this is done, the turrets instantly open fire on Horrigan and usually beat him down to about half of his original hit points before he runs out of ammo for his weapon. Essentially, recruiting Sergeant Granite's team, sneaking to the terminal and activating counter insurgency can win this battle without a single shot fired.
It seems possible to complete Fallout 3 after having killed creatures in only two quests or subquests. This has now been confirmed. Unlike in the previous games, none of the creatures killed are closely related to the central plot nor qualify as major (or even minor) villains.
Although creatures killed solely by companions are not counted as kills by the lone wanderer for the purpose of experience or general stats, since it is relatively easy to have a companion perform any killing that the lone wanderer would like doing, for the purpose of completing the game without killing, we will treat kills by a companion as the same as kills by the lone wanderer.
- However, if you escape the vault as a baby during the Baby Steps quest using the bug described on the page of that quest, you are able to skip your 10th birthday involving the BB gun.
In the quest The Waters of Life, the subquest "Clear Project Purity of any remaining Mutant Threat" requires the character to kill all the mutants in the water purification plant. Although the turrets can be set to attack the mutants, it does not seem possible for the turrets to kill a significant number of the mutants. Project purity contains a total of 13 super mutants and centaurs, all of which must be killed.
It is not possible to complete Fallout 3 with no blood being shed, even with just the minimal amount above. While the player can get through the game as a pacifist, others are not so lucky. It is impossible to prevent Catherine's death (though she dies of natural causes). If one proceeds with the game, Jonas must die, as must either Tom and Mary Holden or the guards killing them. Either Officer Kendall or the radroaches he encounters must die as the player flees Vault 101. The list goes on. While it may be possible for the player to minimize blood spilt by him/her, preventing others fighting is generally impossible. Furthermore, in Take it Back!, the Lone Wanderer must participate in the assault on Project Purity, in which numerous Enclave soldiers are killed. Towards the end of this quest, Colonel Autumn can be persuaded to surrender, at which point, the remaining Enclave soldiers will stop fighting.
In Fallout 3, it is generally harder to hide or to end combat by fleeing, which makes sneaking through several missions very difficult. However, with a good supply of stimpaks, it is surprisingly easy to run through these.
Fallout: New Vegas
It is possible to complete Fallout: New Vegas without the player or any player companions killing any creature - human or otherwise.