He was the President of the Church's Consistorial Court of Discipline in the world Lyra lives in the novel trilogy His Dark Materials.
He wants to abolish Free Will and is very determined to hunt down and kill Lyra, the protagonist, as she is Eve reincarnated and as being Eve, the first woman, Lyra will fall to what Hugh calls "Original Sin." So he sends out a man named Father Gomez to assassinate Lyra with a shotgun to the head.
Later, Hugh travels to Geneva to see the nuclear testing of an interdimensional bomb whose explosion will resonate through every universe and destroy Lyra. Hugh is killed in an invasion on the base before this can happen, but although the bomb does detonate, it doesn't kill Lyra because her mother, Marisa Coulter, took a small lock of her hair which was going to be a vital part of the bomb.
As Lyra opens a gate from the Underworld into the Multiverse, it is presumed Hugh's ghost went through the opening and became one with everything.
Hugh McPhail was an uptight and very business-like man, paying no heed to anything except his ultimate goal of abolishing Free Will. He is the one who started the General Oblation Board, of whom Marisa Coulter was the director, as he wanted to kill off Free Will and Original Sin in every child in his world.