Peter Gosselin Fitzgerald (born October 20, 1960) was the junior United States Senator from Illinois from 1999 to 2005. He is a member of the Republican Party (GOP). He is considered a maverick who is against corruption and pork barrel spending. He previously served in the Illinois State Senate from 1992 to 1998, where he was a member of the 'Fab Five' group of conservatives who often challenged the leadership of the Illinois GOP. The group also included Steve Rauschenberger, Dave Syverson, Patrick O'Malley, and Chris Lauzen.

Born in Illinois, Fitzgerald graduated from Portsmouth Abbey School, a Catholic boarding school on the shores of Rhode Island, in 1978 and from Dartmouth College in 1982. He completed his post-graduate studies as a Rotary Scholar at Aristotelian University in Greece, and earned his law degree from the University of Michigan in 1986.

Fitzgerald's family has been continuously involved in commercial banking since the mid-1940s. His father, Gerald, built Suburban Bancorp, a chain of suburban banks, by aggressively founding and buying banks around the Chicago suburbs, which he sold in 1994 to a subsidiary of the Bank of Montreal for $246 million.