The actor, 40, made the happy announcement in person on an episode of ITV's This Morning, although a spokesperson had revealed the news earlier this week, with Sophie's bump said to be visible during a recent public appearance.
When asked about the new baby by host Alison Hammond, who mentioned that she'd heard the speculation, Benedict said: 'We're expecting our second, yeah', adding: 'I'm going to be there all the way.'
Benedict had been friends with theatre director Sophie for 17 years before their engagement in November 2014. The pair tied the knot on Valentine's Day 2015 in a romantic ceremony on the Isle of Wight, followed by a reception at Mottistone Manor.
They already have one child together - a son named Christopher, often referred to as Kit, who was born in June 2015.
Benedict and his wife Sophie, pictured together at the launch event for his latest film, Dr Strange, where fans spotted her bump
Speaking in November of the same year, Benedict told Vanity Fair: 'Having a baby – it's massive. And on a very unexpected level.'
'Suddenly I understood my parents much more proudly than I ever had before.'
He added that fatherhood had also helped him as an actor - at the time, in his role as Hamlet in a new production of the Shakespeare play.
'I was expecting with Hamlet that it might be a hindrance to be a father, because it's all about being a son,' he explained. 'But it's the opposite. You understand much more about being a son, becoming a father.'
Benedict and Sophie haven't yet revealed the due date of baby number two, or said whether or not they know the gender of the child, but one thing's for sure - we bet Kit can't wait to become a big brother!