When first designated the A427 ran from a junction with the A45 southwest of Rugby through Rugby itself to Clifton upon Dunsmore crossing the A5 through Catthorpe (past what is now the Catthorpe Interchange between the M1 motorway, the M6 and the A14 road).

It then passed through Swinford, South Kilworth, North Kilworth, Husbands Bosworth, Theddingworth, Lubenham and Market Harborough, and from there along its current route to Oundle.

[2] By 1976 the former A4114 road from Coventry via Lutterworth to North Kilworth had taken the designation A427 in place of the earlier route.

The section from North Kilworth and Market Harborough is now part of the A4304.

From West to East its route is: Running through Corby, the A427 meets with the A6003 on the western edge of the town and it has a 1.0-mile (1.6 km) overlap with the A43 in the Weldon North Industrial Estate, where it is briefly dual carriageway.