Merseyrail's new trains will begin to enter the network from Monday after the operator and unions agreed a deal.
Liverpool City Region Mayor Steve Rotheram said talks with unions, which he said were the last hurdle stalling the rollout, have been resolved.
The 52-strong fleet was ordered in 2016 from manufacturer Stadler, but their delivery has been delayed by issues including a factory flood and Covid-19.
The operator said the first train would run on the Kirkby line.