The transport minister announced the project on Thursday
Rail journey times between Manchester and Liverpool are to be speeded up under a £100m plan to electrify the line, the government has said.
The 32-mile line from Liverpool Lime Street to Manchester Victoria - said to be the world's oldest intercity route - currently uses diesel trains.
Transport minister Sadiq Khan said work would begin immediately and would take about four years to complete.
The North West Rail Campaign welcomed the announcement on Thursday.
Work to electrify the line will be combined with other track and signalling improvements to slash minimum journey times from 44 to 30 minutes.
The government said the electric trains would be quicker, quieter, smoother and more reliable than diesels - as well as more environmentally friendly.
"The work begins today to have the world's oldest intercity line electrified, which is great news all round," said Mr Khan.
"Electrification will provide quicker, more comfortable journeys for rail passengers and help boost business in these two great cities.
"The government is investing in our railways, boosting the economy and reducing emissions. This £100m scheme will help us achieve all these aims."
The announcement, made by the transport minister on Thursday, is part of a £1bn electrification scheme across the country.
Roger Jones, of the North West Rail Campaign, hailed the scheme as "great news", but said he hoped the government would deliver its commitment to begin work immediately.
"I like the words 'work is going to start today' because back in 1979 the then government was promising to do electrification, there was a general election, Margaret Thatcher was in and that was the end of that," he said.
"I don't think just knocking 15 minutes off is the be all and end all - what really matters is the frequency of the trains and the fact you can have longer trains.
"To have two cities 35 miles apart without electrification is maddening really. It should have happened years ago."