Both sides last met in April but adjourned negotiations when they failed to reach an agreement.
The row over parent firm Govia Thameslink's plans to introduce driver-only-operated (DOO) trains has caused misery for travellers.
Passenger group Brighton Line Commuters said it welcomed the new talks, but was "sceptical" anything would be resolved.
Shelley Atlas, who runs Brighton Line Commuters, added: "This should have been sorted out many months ago. People have got used to the situation, and many have made other arrangements to get to and from work now. But it's really not acceptable, or satisfactory.
"People are of course sceptical, but this has to be sorted at some point."
The RMT has taken 31 days of strike action over the proposed changes so far.
Spokesmen for Southern and the RMT both confirmed the meeting would begin on Monday.
Members of drivers' union Aslef - also involved in a row with Southern over the same issue - rejected a deal with the train operator in February, and again in April.
Talks between Southern rail and the RMT union are to resume later in a bid to finally resolve the year-long dispute.