Mercedes' career began in 1973 when she won the Grand Final singing contests of both Young Talent Time and New Faces.
In 1981, she released a single titled "Then He Kissed Me", a cover version of The Crystals song, produced by James Freud and the Radio Stars bass player, Mick Prague and Molly Meldrum. It was also performed live on Countdown and Hey Hey It's Saturday.
Mercedes is most widely known for her roles in musical theatre in Australia.
She played the role of Luisa Contini in the 1987/88 original Australian production of Nine, the cast recording of which won an ARIA Award.
Mercedes starred as the alternate Norma Desmond in the original Australian production of Andrew Lloyd Webber's Sunset Boulevard at the Regent Theatre, Melbourne in 1996/1997 alongside Hugh Jackman. She eventually took over the role, giving almost 100 performances.
In 2006 and 2007 she appeared in the musical Pet Shop Boys Re-Interpretered in Melbourne for the Midsumma Festival at Chapel Off Chapel and at the Edinburgh Fringe Festival in Scotland in 2007.
In 2011/12, she played Madame Giry in the Australian production of Andrew Lloyd Webber's Love Never Dies, the sequel to The Phantom of the Opera, at Melbourne's Regent Theatre and at Sydney's Capitol Theatre. A filmed version of this production was released by Universal for screenings around the world and on DVD.
Other roles include The Rocky Horror Show as Magenta (1985) Australian Tour, Cats as Grizabella, Cameron Macintosh Production (1988) at Her Majesty's Theatre Melbourne, Jim Sharman's production of Chess as Svetlana (1990) Regent Theatre Sydney, Forbidden Broadway Kinselas Sydney (1991), Jim Sharman's play Shadow and Splendour as Sophie Lenz for the Queensland Theatre Company and the South Australian Theatre Company (1992) And the World Goes 'Round (1996) Sydney Opera House, Chicago as Mama Morton (1999/2000) Australian/Asian Tour, Fame as Miss Sherman (2000/02) Adelaide Festival Theatre and the Asian Tour, The Vagina Monologues (2001) and Gypsy as Mazeppa for The Production Company (2002).
In November 20, 2004 the Neighbours cast staged the The Rocky Horror Show for the charity Variety and Mercedes became the first actress to play the role of Dr Frankenfurter. She played The Leader in a concert version of Zorba performed by the cast of Chicago at Sydney's Capitol Theatre in 1999.
In 2008/9, Mercedes toured nationally in Menopause The Musical as The Power Woman. Mercedes performed The Songs of James Bond live in concert in 2013 at Melbourne's Athenaeum Theatre, singing classics such as "Diamonds are Forever", "Moonraker", "Kiss, Kiss, Bang, Bang" and "For Your Eyes Only".
In 2014/15, Mercedes played opera star Maria Callas to critical acclaim and a sold out season of the Terence McNally play Master Class at fortyfivedownstairs Melbourne. Mercedes reprised this role in 2016 at The Hayes in Sydney, a return season at fortyfivedownstairs, Geelong Performing Arts Centre, the Whitehorse Centre and the Frankston Arts Centre.
In March 2016, she joined the cast of a new play Taxithi by Helen Yotis Patterson, the telling of Greek women migrating to Australia during the 50's, 60's and 70's. The play is a series of monologues, interspersed with traditional Greek music and songs of the time. The piece resonated deeply with Maria as her own parents' stories of migration resonated within the stories of Taxithi. For the first time in Maria's theatrical career she was given the opportunity to sing in Greek.
Mercedes' first movie role was as Nurse Panicale in the Australian Gothic thriller, Patrick. In the 2013 remake of this film, Mercedes appeared in a cameo role as a doctor. In Head On with Alex Dimitriades, she played the role of Tasia. In 2005, she starred as Ellen in the independent film by Anna Kannava, Dreams for Life. For this role, Mercedes was nominated for Best Actress at the Cypress International Film Festival (2006).
Mercedes is known for two appearances in the cult Australian television series Prisoner. In 1979, she played Greek prisoner Irene Zervos and in 1985 she returned to the series to play another ethnic inmate, Yemil Bakarta. Other roles in major Australian television productions including Homicide, Division 4, Bluey, Special Squad, Inside Running and Whipping Boy. She appeared in the television comedy/variety series Greeks on the Roof as Poppy, the mother of Effie, and in the comedy series Kick as Dora Mavros. She appeared in Neighbours in a recurring role as Lucia Cammeniti.
She appeared as Madam Breda in the first episode of Miss Fisher's Murder Mysteries and played Agape Makrakanis in the television series Fat Tony & Co.Award
Green Room Award 2015 Outstanding Female Performer (Independent Theatre) for Master Class
The Green Room Awards 1987 for Nine the Musical
The Sydney Theatre Critics 1988 for Nine the Musical