Chris Heaton-Harris said £2.5 million of Government funding will pay for CrossCountry to operate trains with more carriages.
Services running through Birmingham New Street station between Nottingham, Leicester and Cardiff will get more than 5,000 additional seats per week from May.
A further 15,000 weekly seats are planned for other routes such as Cambridge-Stansted Airport from mid-2021.
This should also including route serving Stafford and Wolverhampton station, between Manchester and Bournemouth.
The carriages will come from West Midlands Trains, which is receiving new carriages for West Midlands Railway services.
It comes as operator West Midlands Trains has faced scrutiny over its performance after delays and disruption have dogged services
Just 58 per cent of CrossCountry passengers are satisfied with the level of crowding on trains, the latest major survey by watchdog Transport Focus suggested.
This was the second-lowest score of all operators, above only TransPennine Express which received 57 per cent.
CrossCountry operates long-distance trains, with routes stretching from Penzance to Aberdeen.
The funding follows the Department for Transport's decision last summer to extend the Arriva-owned operator's franchise to October 2020.
Investment will also be made to expand CrossCountry's seat reservation service to allow passengers to reserve a seat on most services.
Mr Heaton-Harris said: "Investing in transport is essential to levelling up the country, as we look to modernise our rail network and restructure the industry to put passengers at the heart of the railway.
"But we want to fund benefits to address pressing needs and improve journeys for passengers in the short-term, as well as in the future.
"More seats mean more people can travel, increasing access to opportunities and better connecting our regions."
CrossCountry managing director Tom Joyner said: "We are delighted to now be able to get on and deliver these benefits for our customers, with improvements to the journey experience and three new community groups to bring our train services closer to the places we serve.
"Most importantly, many of our trains have become increasingly busy as more and more people choose rail for their journeys.
"This delivers the biggest increase in seats for our services in more than 13 years, helping customers enjoy a relaxing and comfortable journey every day.
"These improvements will deliver an immediate boost for rail users in the Midlands, with the promise of even more to come on other routes in the near future."