Deadpool's immortality comes from his extreme healing factor, which constantly replaces his damaged cells with healthy ones at such an absurd rate that he's actually immune to telepathy because his brain cells are being repaired faster than any telepath can mess with his mind.

Why did Thanos make Deadpool immortal?

Months later, T-Ray, now an agent of Thanos resurrects Deadpool, who has been killed in a fight with Weapon X, using an artifact Thanos gave him to create many copies of Deadpool. Thanos is jealous of Deadpool's relationship with Death and T-Ray is to "curse him with immortality" so that he may never see Death again.

Is Deadpool actually immortal?

Deadpool is effectively immortal, although he has died several times. He is still alive 800 years in the future when the new X-Force encounters him. ... He revealed that the only thing keeping Wade alive was his "spell of darkest necromancy".