Stage 1 was prioritised and taken forward and designed by the County of Lanark, opening to traffic in April 1967 after some construction delays. This provided a dual carriageway link from Whirlies Roundabout to Crossbasket. The eventual cost was £600,000, almost double the initial estimate of £382,000. Contractor was James, Anderson and King.

 

Stage 2 from Crossbasket to Auchinraith was completed eleven years later in October 1978. Scottish Development Department grants were provided in 1973/74 to allow for the removal of coal bings along the route. The eventual cost was £5.2 million. Design work was undertaken by Lanark County and Strathclyde Regional Council's. The main contractor was Murdoch MacKenzie Ltd.

 

Stages 3A, 3B and 4 completed the most difficult section of the route from Blantyre to Raith Interchange and include several large structures in the Whistleberry area. Great care had to be taken near the existing Bothwell Bridge and property acquisition considerably added to the overall cost of the scheme which ended up costing £12.2 million. The project was design by Strathclyde Regional Council and constructed by Murdoch MacKenzie Ltd. It was completed on December 15th 1983. On completion, the A725 number was extended to East Kilbride.  

 

As Paul Veverka from the Blantyre Project explained in 2016, “Great care had to be taken around the old Bothwell Bridge protecting it fully as parts of it dated to the 15th century. The Bothwell Bridge was built between 1400 and 1486. According to the expressway architects, evidence of that original bridge is still located within the core of the existing Bothwell Bridge. During the Expressway construction, the contractors were able to dispel a myth that somehow a 5th arch would be under the road approaches. This was not the case and the bridge was confirmed as only having 4 arches.”

 

The section through Raith Interchange was considerably upgraded between 2014 and 2017 with the provision of a grade separated underpass for through traffic. Traffic congestion was occurring at peak times only a few years after it was completed, with the Scottish Office commissioning improvement studies as early as 1992. Part-Time traffic signals were installed during the 1990s, eventually becoming permanent at the ends of the M74 slip roads.

 

Minor modifications have been made along the route in recent years. In the mid-1990s a link to Nerston was added to remove traffic from Whirlies Roundabout and additional slip roads were added to aid access to the Hamilton International Business Park at High Blantyre. In the mid-2000s the Diamond Interchange was remodelled as part of the expansion of the Strathclyde Business Park. In 2017 east facing slips to the new offline section of M8 motorway were added and the junction with North Road and A8 at Shawhead were completely rebuilt.

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The short section of A725 from Shawhead to the A89 near Coatbridge town centre is a non-trunk road maintained by North Lanarkshire Council. It was dualled in phases from the early 1970s to the 1990s.