Prior to the construction of Glasgow’s motorway and dual carriageway system, the A726 was one of the conurbations most important routes. In the mid-1930s, the number was assigned to the road linking the A74 at Kirkmuirhill with the southern terminal of the Erskine Ferry. It interchanged with other routes of historic importance including the A71, A723, A77, A736 and A737.

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Changes to the original road began in the late 1950s when its route through East Kilbride was considerably altered. Construction of the New Town resulted in the completion of an extensive new roads system and the A726 number was assigned to the Queensway, an east to west dual carriageway immediately south of the new town centre. It interchanges with the A725 Kingsway at Birniehill Roundabout. A short section of Strathaven Road was also upgraded at this time.

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The 1960s saw substantial changes in the Paisley area with construction of the M8 Renfrew Bypass scheme and new Glasgow Airport at Abbotsinch. The original Barnsford Road was altered to suit the airport boundary and interchange with the motorway at St. James Interchange. Around this time, sections of the A726 in the south of Glasgow from Hurlet to Eastwood Toll were upgraded to dual carriageway.

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Construction of the Erskine Bridge and Erskine New Town in the 1970s led to an upgrade at its western end. Over two miles of new and improved road were built, with the road pulled north to interchange with the A898 and M898 at the south end of the bridge. The section through Erskine was future proofed to allow for eventual widening to dual carriageway standards. This was dropped as plans for the town were scaled back, though visible signs remain on the ground today.