The draw for the semi-finals was made at St. Mary's Stadium on Wednesday night after the Saints knocked out eight-time winners Manchester City. Nottingham Forest beat Wolves 4-3 on penalties in the other semi-final after a 1-1 draw at the City Ground.
On Tuesday night, Eddie Howe's Magpies booked their place in a first cup semi-final in 18 years with a 2-0 win over Leicester City at St. James' Park thanks to goals from Dan Burn - his first for the club he grew up supporting - and Joelinton, while Manchester United beat League One Charlton 3-0 at Old Trafford.
The Magpies, who have beaten three Premier League sides to reach this stage, have never won the competition and are looking to end a 68-year wait for a domestic trophy.
The first leg tie, at St. Mary's, will be played in the week commencing 23rd January and the second leg, on Tyneside, will be played in the week commencing 30th January.
Southampton came out on top in the only previous League Cup meeting between the two sides, winning 4-1 on the South Coast in a third round tie in the 1968/69 campaign.
Ticket details for both games will be announced in due course.