The Principality Stadium's gates open at 17:30 BST on Tuesday and Wednesday, with the support act starting at 19:00 and Coldplay on stage at about 20:30.
Those driving to Cardiff are urged to use a park-and-ride at Cardiff City Stadium.
Visitors by train have been strongly advised to leave plenty of time, with the network expected to be busy.
The Principality Stadium, which will have its roof open for the concert, has issued new policies on bringing bags into the stadium, as well as information on prohibited items and body searches.
Only small bags, no larger than 35cm (13in) x 40cm (15in) x 19cm (7in), will be allowed into the stadium.
A queuing system will run at Cardiff Central Station.
Queen Street Station will close at 21.45.
All train passengers are advised to buy a ticket before they board a train.
Road closures
Scott Road and Park Street will be closed earlier on each day to allow for a barrier system to be put up on the approach to gate five.
A full programme of city centre road closures will be in place from 18:00 until 23:30, including:
The following roads will be closed in their entirety:
Duke Street, Castle Street, High Street, St Mary Street, Caroline Street, Wood Street, Central Square, Westgate Street, Quay Street, Guildhall Place, Golate, Park Street, Havelock Street and Scott Road.
The following roads will be closed from 21:00 until 23.30:
Saunders Road from the junction with St Mary Street, Customhouse Street, throughout its length and Penarth Road, from the junction with Saunders Road to the entrance leading to the back of Cardiff Central station.
Buses
Buses will be diverted out of the central city centre bus stops.
Those displaced from stops within the closure will relocate to either Churchill Way for the east, Greyfriars Road, for the north, and Tudor Street, for the west.
Cardiff city centre roads will be shut as 60,000 people head to the capital for each of Coldplay's two concerts.