ScotRail's express trains will offer free wi-fi by the end of December 2013, thanks to £2million investment from the Scottish Government.
The cash will fund the installation of wi-fi equipment on all 59 of ScotRails class 170 trains.
The fleet operates between most Scottish cities and in the Fife and Stirling areas.
At present four class 170s offer wi-fi connectivity, fitted as part of a successful trial launched by Transport Minister Keith Brown in the summer. Customer feedback revealed that 77% of users were satisfied with the speed and performance of the wi-fi, with personal and business use found to be 72% and 28% respectively.
From March 2013 the number of wi-fi trains in passenger service will steadily increase, at a rate of five or six each month.
The free service is designed to allow access to email, web browsing and social media sites such as Facebook and Twitter.
ScotRail is also drawing up plans to provide train running information and other useful services on its wi-fi landing page.
Announcing the roll-out of the scheme, Mr Brown said: We have an absolute commitment to bringing better connectivity to every corner of Scotland and I have been highly encouraged by the success of ScotRail pilot scheme.
A major challenge for the transport industry is embracing new technologies to meet the demands of passengers and help them get on with their ever more busy lives while travelling.
Just like our roads and railways, the internet is a vital part of Scotlands infrastructure. It is essential that people throughout Scotland have online access to enable our economy to thrive, which is why we are already forming plans to further expand wi-fi provision across the rail network.
Steve Montgomery, managing director of ScotRail, said: We are confident the installation of free wi-fi will be warmly welcomed by our customers. More journeys are made on our class 170s than any other of our trains, so it makes sense to begin the roll-out on this fleet.
We will be fitting wi-fi during planned weekend maintenance, to avoid taking trains out of service.
The move has been welcomed by business leaders. David Birrell, chief executive of Edinburgh Chamber of Commerce, said: "Many of our Edinburgh-based members do business throughout Scotland which inevitably means some travel to and from meetings.
Increasing wi-fi access on trains will undoubtedly enhance the ability for business people to stay connected and therefore improve productivity during transit. That can only be welcomed."
The contract to install wi-fi has been awarded to Icomera, one of two companies who took part in the trial in the summer. It is regarded as a leader in the provision of wi-fi to UK rail operators.
