The 25-year-old is in the final stages of sealing a move to the south coast after fielding interest from other Premier League clubs, including Bournemouth.
Maitland-Niles will join Southampton for the rest of the 2022-23 campaign and also extend his Arsenal contract - due to expire next summer - by a year.
The loan deal is also expected to include the option for a permanent transfer in 2023.
Maitland-Niles came through Arsenal’s academy as a youngster but he has failed to establish himself in the first team.
He has been repeatedly loaned out by the club and spent the second half of last season at Jose Mourinho’s Roma.
Maitland-Niles has previously operated in midfield and at full-back during his spells at different clubs and it remains to be seen what Southampton view as his most effective position.