Below is a list of famous Jewish Catholics (or Catholic Jews, or Hebrew Catholics).
"Jewish Catholics" are simply people that are both Catholic and Jewish. Many of these individuals had one Catholic parent and one Jewish parent. (It does not matter whether it was the mother or father that was Catholic or Jewish.) Other individuals on this list had two Jewish parents (or only one), but they converted to Catholicism during their life.
There are exceptions, of course, but for the most part, Jewish Catholics do not practice the religion of Judaism in any meaningful way. Their "Jewishness" is merely an ethnicity, a fact of birth. These individuals may or may not have any meaningful self-identity as Jews. Generally speaking, if Jewish Catholics practice any religion, that religion is Catholicism.
The list of Jewish Catholics may also include people who were fully Catholic, but who converted religiously to Judaism.
Sean Penn - actor, movie star (devout Catholic mother; non-observant Jewish father)
Fritz Lang - famous German film director (Catholic father; mother was Jewish convert to devout Catholicism; Fritz raised as a devout Catholic)
Roger Corman - famously successful and prolific independent/low-budget feature filmmaker (half Jewish; raised Catholic)
Erich von Stroheim - famous Austrian-born actor-director (both parents Jewish; convert to Catholicism while young; lifelong active Catholic)
Roman Polanski - film director (both parents agnostic Jews; Roman converted to Catholicism at age 10, active until age 15; has some Jewish ethnic identity)
Oliver Stone - film director (lapsed Catholic mother; non-observant Jewish father; raised Episcopalian; converted to Buddhism as adult)
Adam Goldberg - actor; Saving Private Ryan, etc. (lapsed Jewish father, lapsed Catholic mother)
Barry Gifford - poet, novelist, playwright, screenwriter (Jewish father; Irish Catholic mother; anti-Catholic as an adult)
Fiorello LaGuardia - progressive, liberal, powerful Republical mayor of New York City (served 1934-1945) (son of Jewish and Italian immigrants)
Douglas Fairbanks - actor, silent screen legend (Jewish father, Catholic mother - both lapsed; Fairbanks was never active in either faith)
Helena Bonham Carter - actress; Planet of the Apes (2001); Fight Club (1999); Howards End (1992); other Merchant Ivory films; etc. (mother was a Jewish convert to Catholicism)
Robert Novak - conservative columnist and TV commentator (Jewish convert to Catholicism)
Harrison Ford - actor; "Han Solo" in Star Wars; Indiana Jones, Witness, Air Force One, etc. (Jewish mother)
Theodor Adorno - German philosopher, composer, (ethnic Jewish father became Protestant; Catholic mother)
Simone Weil - French philosopher (converted to Catholicism)
Ludwig Wittgenstein - Austrian philosopher (father's parents became Protestants, mother was Catholic)
Lindsey Vuolo - Playboy Playmate (Jewish mother, father converted from Catholicism)
Bernard Nathanson - former abortionist (doctor who performed abortions) turned pro-life activist; rejected abortion on scientific grounds (Jewish convert to Catholicism)
Karl Stern (1906-1975) - neuropsychiatrist and author; author of Pillar of Fire, etc. (Jewish convert to Catholicism)
Israel Zolli - Chief Rabbi of Rome (converted to Catholicism)
Jim Croce - rock musician whose hits include "Bad, Bad Leroy Brown" (raised in devout Catholic family; converted to Judaism when he married Ingrid Jacobson)
Amanda Bynes - teen actress, Nickelodeon TV show host; All That; The Amanda Show; Big Fat Liar; What a Girl Wants; etc. (Catholic father, Jewish mother)
Anne Meara - actress, comedian; married to actor Jerry Stiller, father of actor Ben Stiller (Irish Catholic convert to Judaism)
Arlo Guthrie - folk singer; composer of "Alice's Restaurant" (Jewish mother; convert to Catholicism)
Dick Morris - former advisor for Pres. Bill Clinton; political author
Don Adams - actor best known as the fumbling spy "Maxwell Smart" on the TV series Get Smart (Irish Catholic mother, Hungarian Jewish father, raised Catholic)
Dutch Schultz - prohibition era mobster; real name: Arthur Fleggenheimer (Jewish convert to Catholicism)
Franz Schreker - Austrian-German composer (Jewish father)
Harry Connick Jr. - singer, actor (ethnically part Jewish; raised Catholic, practicing Catholic)
Hedy Lamarr - actress, inventor of the first form of spread spectrum, a key to modern wireless communication
Hermann Broch - German novelist; The Death of Virgil
Hugo von Hofmannsthal - Austrian German-language poet and dramatist
Jacques Offenbach - French composer
Jerry Orbach - actor; Law and Order (Jewish father)
Johann Strauss - composer known as "The Waltz King"; Blue Danube, Acceleration Waltz, Emperor Waltz, etc
Jorge Sampaio - president of Portugal (Catholic, but son of a Sefaradi Jewish mother)
Julianna Margulies - actress on TV drama ER (Jewish father, raised Catholic by mother)
Kevin Kline - Oscar-winning actor; Sophie's Choice, A Fish Called Wanda, Dave, French Kiss, etc. (Jewish father)
Marianne Faithfull - British singer, actress (Jewish convert to Catholicism at her school's request)
Michael Bennett - choreographer (Jewish mother)
Michael Landon - actor best known as "Pa" on Little House on the Prairie TV series; real name: Eugene Maurice Orowitz (Jewish father, Catholic mother, baptized Catholic)
Paulo Costanzo - actor; sitcom Joey; films Road Trip, 40 Days and 40 Nights, etc. (Jewish mother)
Phoebe Cates - actress; Fast Times at Ridgemont High, etc. (real name: Phoebe Katz)
Pierre Salinger - white house press secretary, 1961-64 (Jewish father)
Tom Baker - actor; played the Doctor on BBC series Doctor Who from 1974 to 1981
Wolfgang Pauli - discoverer of the Exclusion Principle and the neutrino (Jewish father, half-Jewish mother, converted from Judaism to Catholic, but later left Catholic Church)
Yves Montand - famous French actor/singer
Robert De Niro - actor (lapsed Catholic father and an atheist Presbyterian-raised mother; possible Jewish ancestry)
Christopher Columbus - explorer who led Europians to American continent (possibly part-Jewish)
Famous Jewish/Catholic Couples:
George Burns and Gracie Allen: George Burns (a non-observant Jew) and Gracie (a devout Catholic) were regarded as having one of the great marriages of Hollywood history
Alan Alda and Arlene Weiss: Alda (actor best known as "Hawkeye Pierce" on TV's M*A*S*H), was a devout Catholic when he married Weiss, who was an observant Jew. At the time their first child was born, Alda ceased Catholic Church activity and his wife mostly lapsed from Judaism. They raised their children in "a loosely associated 'free thought' style of religion, the family nevertheless celebrates religious holidays--both Catholic and Jewish"
Fred Zinnemann and Renee Bartlett: film director Zinnemann was essentially a non-observant Jew. Probably partially because of the influence of being married to a Catholic, he made some profoundly Catholic films, including The Nun's Story (1959) and A Man for All Seasons (1966). His films The Seventh Cross (1944) and Julia (1977) are considered great Jewish films.
Martin Scorsese and Laraine Marie Brennan: Before studying film at New York University, film director Scorsese had dropped out of Seminary where he had intended to become a Catholic priest. His first wife (Brennan) was Irish-Jewish. They were married on 15 May 1965 in a traditional Catholic ceremony at St. Patrick's Cathedral soon after Scorsese's graduation from NYU. They had 1 child before they divorced. Scorsese has said his marriage had a lot to do with his rejection of his parents' values and his turning away from formal activity in Catholicism.
Interesting Novel: A God in Ruins, by Leon Uris: It's 2008, and the Democratic candidate for the presidency is Jewish--but, as an orphan who was raised Catholic, he doesn't even know it. Is America ready for a Jewish president? We'll find out in this long awaited novel from an author known for his historical sagas usually centering on the Jews or the Irish. This time he gets to deliver both in the same hero.