The actor nominated for an Oscar for Sunday Bloody Sunday was Peter Finch.

Why this is the answer

The film received Oscar nominations in 1972, including one for Best Actor in a Leading Role , and that nomination went to Peter Finch. A second acting nomination that year was for Glenda Jackson, but the actor most commonly identified for the film’s Oscar acting nod is Peter Finch.

Related note

The movie also received a Best Actress nomination for Glenda Jackson and additional nominations beyond the acting categories.