Sam, who plays Finnick Odair in the films with Jennifer Lawrence, made no official announcement but it was clear for everyone on the red carpet to see the loved-up pair are expecting a new addition to their family.
And they are proud as punch.
The 29 year old married Laura Haddock, 30, who played Alison in the Inbetweeners film, in a private ceremony in July 2013.
The Ipswich-born actor has previously said about his wife; 'She's my female counterpart is the best way to describe her. She is my mum. She reminds me of my mum so much which I think - a guy will know, right? It's important. Your mum knows like everything.'
The pair started dating in 2011 after meeting at a casting for a film and discovering they shared an agent.
'I didn't know anything about her other than that her name was Laura, she was very attractive and she seemed lovely.'
The next morning they bumped into each other at a London tube station and after their 'instant spark' Sam tracked her down on Facebook.
'I went home, woke my friend up at 7am and said - I just met the girl I want to marry. I love this girl like, I love her. She is perfect.'
The Pirates Of The Caribbean star gushed about falling more in love with the mum-to-be 'every five seconds'.
'Getting married was easily one of the greatest achievements of the past 12 months. To have a wife with such wondrous, creative imagination, who planned every inch of it, made the day all the more special.'
No further details about the baby, including the due date, have been announced yet.