The 23-year-old came through the ranks at St Mary's Stadium and has gone on to make 205 first-team appearances for the club, scoring 12 goals.
In 2016, Ward-Prowse also captained England Under-21s to their first Toulon Tournament victory since 1994.
According to The Sun, the Clarets are in pole position to sign Ward-Prowse permanently, despite Watford having been in the running for the player's signature.
The Hornets were believed to have made a loan offer for Ward-Prowse, with Southampton seemingly not interested in such an arrangement.
Ward-Prowse featured in 30 Premier League games last season, scoring three times.