The government has pledged £20 million to help Southern rail "get to grips" with its poor performance.
It has announced a series of measures including the appointment of a new "project board".
The move comes after months of disruption to services on the network because of a dispute over the role of guards and staff shortages.
Former Virgin Rail chief operating officer Chris Gibb will head the new project board.
He will work with the train operator, the Department of Transport and Network Rail, to achieve a "rapid" improvement in services.
On Tuesday, the company said it would reinstate over 100 services from a total of 300 that were cut from the timetable in July.