Ivanek was born Željko Šimić-Ivanek in Ljubljana, PR Slovenia, FPR Yugoslavia. In 1960, Željko, his mother and younger brother, Ivan, immigrated to Palo Alto, California, where his father was studying for his PhD in electrical engineering at Stanford University.

After a two-year stay, in 1962, the family moved back to Yugoslavia for five years and then returned to Palo Alto in 1967. Having performed in numerous community theater plays in the San Francisco Bay Area, he graduated from Ellwood P. Cubberley High School in Palo Alto in 1975. Ivanek graduated from Yale University majoring in theater in 1978 and afterward attended the London Academy of Music and Dramatic Art.

Ivanek has worked extensively on the stage. In 1982, he originated the role of Hally in Athol Fugard’s play “Master Harold”…and the Boys. He appeared in the U.S. premieres of Cloud Nine (for which he earned the 1981 Drama Desk Award for Outstanding Featured Actor in a Play) and The Pillowman. He performs frequently on Broadway and has been nominated for three Tony Awards, for his performances in the original production of Brighton Beach Memoirs, in Two Shakespearean Actors, and in a revival of The Caine Mutiny Court-Martial, alongside David Schwimmer and Tim Daly.

Ivanek has received recognition for his on-screen work. In 2008, he was awarded the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series for his performance in the role of Ray Fiske on Damages.

In 2012, he portrayed Dr. Stafford White in the Fox drama The Mob Doctor. As of 2014, he has supporting roles in several shows on broadcast and cable television, including the NBC drama series Revolution, where he plays the recurring roles of Dr. Calvin Horn and an illusory nanotech avatar of Horn; the USA Network drama Suits; the Cinemax drama Banshee; and the FX series The Americans.