Zach’s career in television began in the mid ‘80s with two appearances on Kate and Allie  as Studio Engineer “Bob Barsky.”  He continued to be cast in supporting roles in various iconic ‘80s shows.  In A Man Called Hawk, he played the partner in crime of a character played by Wesley Snipes, in The Equalizer, he menaced Maureen Stapleton, and in Miami Vice, he was a meddlesome emissary from the top brass.  In 1988, NBC cast him in his first series regular role — Sonny Franks, the thorn in the sides of the elegant restauranteurs of Tattingers.  The show was short-lived, however, and Zach returned to the theatre, with the occasional stint on Law and Order, a show in which, over twenty-some years, he played six different roles.

In 1996, as Zach was performing in A Question of Mercy at the New York Theatre Workshop, ABC cast him in C16:FBI in the series regular role of Jack Dirado, a veteran detective working in a special crimes unit under the leadership of a supervisor played by Eric Roberts.  The work took Zach to Los Angeles, where, after the series’ cancellation, he decided to stay, but not before a sojourn in Chicago, where he played Ivan in Yazmina Reza’s Art at the Royal George Theatre.  In the ensuing years, Zach alternated among theatre, film and television roles.  Appearances on many of the successful shows of the 2000s followed — shows such as The Guardian, The X-Files,” and perhaps most memorably, the first season of 24, in which he played “fixer” Carl Webb.

 In 2004, he again secured a series regular role, this time on USA Network in Touching Evil, playing boss to Jeffrey Donovan and Vera Farmiga.  And again, despite critical acclaim, the show was short-lived.  Months later, Zach was asked to do a role on Deadwood, one that was described to him as a one day guest star appearance in which his character Andy Cramed brought the plague to town.  Having worked with David Milch on  NYPD Blue, he was quick to accept.  One episode led to another, and his role of Andy Cramed became more intrinsic to the plot line of the now legendary show.  However, he was not a contract player, and when New York sent forth the siren song of theatre, he succumbed and spent a summer playing Dick Cheney in David Hare’s Stuff Happens.  After that event, it became clear that he belonged back in New York City, and that fall filmed his most compelling episode of Law and Order, Bible Story.

By 2008, he was back on Broadway, playing Beethoven in 33 Variations.  It was then that he auditioned for a new show called The Good Wife and was hired for the guest role of a lawyer in the central firm named David Lee.  The character was memorable and became a integral part of the team.  With the fifth season, Zach was made series regular and enjoyed playing the irrepressible Mr. Lee for the remainder of the series.  At the end of his engagement with The Good Wife, Zach appeared in featured guest roles on Chicago PD and Blind Spot.

In 2018, Zach was cast in the recurring role of Ed Ferratti, incumbent mayor of NYC and candidate for re-election, in the long running series Ray Donovan.

In the same year, a fateful interview with Alex Garland, director of Ex Machina and Annihilation, led to Zach being cast as a series regular in Garland’s television show for FX on Hulu, Devs.    Zach reconjured The Good Wife's David Lee in the fourth and fifth season of Paramount+'s The Good Fight.

Zach Grenier’s career began in the theatre.  As a young actor, he toured with Boston-based Little Flags Theatre, acting and playing guitar in towns throughout the country in two shows, The Furies of Mother Jones and Winds of People. Subsequently, he appeared as Jacques in a Boston Shakespeare Production of As You Like It, and months later, played the leading role of the Captain at Portland Stage in Play Strindberg.

In 1978, he moved to New York City to pursue a stage career.  It was a challenging time, but he was fortunate enough to obtain the all-important Actors' Equity card by performing with what was then called Performing Arts Repertory Company, or PART, and what is now known as Theatreworks.  He toured with the musical Teddy Roosevelt, playing Roosevelt’s rival New York Senator Chester Conklin.

He made an important theatrical connection by studying with Paul Austin, which led to him joining Ensemble Studio Theatre.  Ensemble Studio Theatre (EST) became his artistic home, and he performed there in three of the EST marathons in Water Music by Michael Erickson, Cross Patch by David Mamet, and Death and the Maiden by Susan Kim, as well as participating in numerous readings and workshops.  With EST providing a base, Zach pursued theatre work in a variety of venues.  In this period, he performed at Hartford Stage in The Tooth of Crime, the Alley Theatre in Hunting Cockroaches, and toured in Citizen Tom Paine in a production that originated at the Williamstown Theatre Festival.

He also appeared in New York experimental theatre as Baal in the Brecht play by that name, in Richard Foreman’s The Cure, Jeffrey Jones’ Der Inca von Peru and Tomorrowland, Kathy Acker’s Birth of the Poet, directed by Richard Foreman, and Mac Wellman’s Sincerity Forever.  In 1988, he performed multiple voice roles, as well as the on-stage character Sid Greenberg in Eric Bogosian’s Talk Radio at the Public Theatre.  His chameleon tendencies next proved useful in the Broadway production of Larry Gelbart’s Mastergate, in which he played all four lawyers in the play.  He worked with Julie Harris in Tim Mason’s The Fiery Furnace at Circle Repertory Theatre and Dame Harriet Walter in Three Birds Alighting on a Field at the Manhattan Theatre Club.  He originated the role of Dr. Chapman in David Rabe’s  A Question of Mercy at New York Theatre Workshop, a performance that earned him an Outstanding Artist honor from the Drama League. While he was performing in that play, he was cast in ABC’s C16:FBI, and he was off to Los Angeles.

Between television and film engagements, Zach takes every opportunity to return to stage work.  His portrayal of Dick Cheney in David Hare’s Stuff Happens at the New York Shakespeare Festival was recognized with an Ensemble Award by the Drama Desk and a Drama League nomination for the Ensemble.  It was not long after that inspiring experience that he found himself cast as Beethoven in Moisés Kaufman’s 33 Variations at La Jolla Playhouse.  These theatrical experiences were the impetus for a move back to the NYC area.  Shortly after his return, he found himself back at EST in Vern Thiessen’s Lenin’s Embalmers.  Later that year, 33 Variations moved to Broadway, with Jane Fonda leading the cast. Zach’s performance as Beethoven brought him a Tony Award nomination.

Since being back on the east coast, Zach has twice shared the Roundabout Theatre Company’s Broadway stage with Frank Langella -- in Robert Bolt’s A Man for All Seasons and Terrence Rattigan’s Man and Boy. He has also worked three times at the Atlantic Theater Company — in Moira Buffini’s Gabriel, John Patrick Shanley’s Storefront Church, a performance that garnered him a nomination for a Lucille Lortel Award, and Rajiv Joseph’s Describe the Night.  During the 2015 hiatus of The Good Wife, he played Mephistopheles to Chris Noth’s Faustus in Doctor Faustus at the Classic Stage Company.

A major career highlight was the role of Willy Loman in Death of a Salesman at the Pittsburgh Public Theater.

Zach continues to regularly employ his theatrical talents by working for Bryan Doerries’ Outside the Wire group, giving readings of Ancient Greek plays for military service people and other survivors.  In 2018, he appeared in Antigone in Ferguson, a Theatre of War production under the aegis of the Harlem Stage