Story Contracting has replaced Carillion as the main contractor for platform extension works at Edinburgh Waverley station.
Story confirmed in a statement it had been awarded the contract by Network Rail.
Original contractor Carillion began work on the £23m project in 2017 before its collapse in January of this year.
Story has previously been sub-contracted by Carillion to deliver elements of the works.
It will include platform extensions, building refurbishments, installation of walkways and escalators.
The project, which is in preparation for new, longer electric trains, is expected to last for 12 months.
Story also sought to allay fears raised recently by a union over workers' rights by stressing that former Carillion staff who had been working on the project would be joining the works team as direct employees.
Unite had said the new contractor must not use "umbrella companies", saying they "exploited" workers.
Umbrella firms process wages on behalf of companies who do not want to employ staff directly.
This can mean workers end up paying excessive administrative fees to get their wages as well as being liable for their employers' national insurance.
In its statement, Story said it would manage the project "in line with their normal operating and management procedures".
It continued: "This will involve Story Contracting's full-time employees managing and working on site with, where needed, a select number of specialist sub-contractors.
"In addition, we have been in discussion with former Carillion staff who are working on the scheme and Story are delighted that they have agreed to join our team as direct employees, bringing with them a wealth of experience and working knowledge of this prestigious project."
The company added: "Story Contracting continue to invest heavily in their workforce who we employ directly, and not through umbrella companies, and our team on Waverley will ensure a smooth handover of the project."