The Glasgow Airport Rail link (GARL) first became a recognised idea during the mid 2000s. The idea is fairly simple. Glasgow Central to the airport, with a stop at Paisley Gilmour Street. The proposal also involved constructing a new rail spur branching off the existing Paisley corridor on the Gourock line, around Paisley St James'. With nearly 2 kilometres of new track. The GARL was formally approved by the Scottish Parliament in 2007 through the Glasgow Airport Rail Link Act. The project was managed by Transport Scotland and backed by the then Scottish Executive (now Scottish Government).  This would have been a Scotrail service every 15 minutes from central, journey time about 16 minutes. 

It was first cancelled in 2009 by the Scottish Government due to budget cuts, rather than it being postponed. Finance Secretary at the time John Swinney (now the First Minister) saying rising costs and competing spending priorities, including the new Queensferry Crossing as reasons for withdrawal of funding.

After the cancellation of the original GARL project in 2009, pressure remained to improve public transport links between Glasgow city centre and the airport. In 2016, a new proposal was put forward by Renfrewshire Council and Glasgow City Council as part of the £1.13 billion Glasgow City Region City Deal: a tram-train link.  Following the same route as the first rail link.

In 2022, the concept of the Clyde Metro was announced as part of Scotland’s second Strategic Transport Projects Review (STPR2). The Clyde Metro is a long-term vision for a multi-modal mass transit network serving the Glasgow region, including a potential link to Glasgow Airport.