Peter O'Brien may refer to:

• Peter O'Brien (actor)
• Peter O'Brien, 1st Baron O'Brien
• Peter O'Brien (filmmaker)
• Peter O'Brien (politician)
• Pete O'Brien (first baseman) (born 1958), MLB first baseman, 1982-1993
• Pete O'Brien (1900s second baseman) (1877-1917), MLB second baseman, 1901-1907
• Pete O'Brien (1890s second baseman) (1867-1937), MLB second baseman, 1887-1890

[ Source: Wikipedia ]