At the Guardians of the Galaxy premiere in Los Angeles on Monday, the Star Trek actress appeared to let her dress - which included a sheer floral top half, a shimmery skirt and a T-shaped belt - do the talking as she looked to have a blossoming baby bump.
Her publicist later confirmed the news to The Hollywood Reporter.
Zoe wed Marco in a secret ceremony in September. The 36-year-old confirmed her new marital status in December during an appearance on the Jimmy Kimmel Show.
"I got married in England," Zoe revealed.
The happy couple managed to keep their nuptials a well-guarded secret from the public eye, but an insider confirmed the news in September.
"It was super small but very romantic and beautiful," a source told Us Weekly, adding that the couple had "known each other for a long time" and had "great chemistry".
Zoe was previously engaged to actor Keith Britton, but they split after 11 years together. She was then in an on-off relationship with Bradley Cooper which ended in January 2013, but the couple looked to be on friendly terms as they shared the Guardians of the Galaxy red carpet together.
The actress, who also starred in the box office smash Avatar will be expecting another international hit in Marvel's latest which is released in the UK on 31 July.
Zoe, who is a brand ambassador for beauty brand L'Oreal, walked the red carpet in May at the Cannes Film Festival with Marco - only weeks after the couple made their first red carpet appearance together at an AOL event in New York.
Marco was there to support Zoe, who took to the stage to talk about her involvement in AOL show My Hero, of which she is executive producer.
Earlier in 2014 she signed a three-film deal with James Cameron to star in the sequel to 3D behemoth Avatar, and she is also expected in further Star Trek films.