MTG Keyword Rules — Comprehensive Rules Glossary

Lifelink is a static ability.

Damage dealt by a source with lifelink causes that source’s controller, or its owner if it has no controller, to gain that much life (in addition to any other results that damage causes). See rule 120.3.

If an object is no longer in the zone it’s expected to be in as an effect causes it to deal damage, its last known information is used to determine whether it had lifelink.

The lifelink rules function no matter what zone an object with lifelink deals damage from.

If multiple sources with lifelink deal damage at the same time, they cause separate life gain events (see rules 119.9–10). Example: A player controls Ajani’s Pridemate, which reads “Whenever you gain life, put a +1/+1 counter on this creature,” and two creatures with lifelink. The creatures with lifelink deal combat damage simultaneously. Ajani’s Pridemate’s ability triggers twice.

Multiple instances of lifelink on the same object are redundant.