The A6137 leaves the A198 at a 90-degree bend in the village of Aberlady on the East Lothian coast, and goes generally southeastwards to Haddington, the county town. In its length of about 5 miles it first runs level, then climbs increasingly steeply to its summit on a shoulder of the Garleton Hills, then falls into the valley of the River Tyne. Apart from 30 mph limits in the urban areas at each end, the road is NSL throughout in the open country between.
The road was originally the northern end of the B6369 and gained its present number in 1935.
Aberlady - Haddington
Heading south on the A6137
Shortly after leaving Aberlady the A6137 goes over the line of the now-closed spur railway from Longniddry to Gullane, then in a mile or so passes under the ECML and reaches a roundabout where the B1377 between Longniddry and Drem crosses. From this point the road climbs to the ridge ahead, in about a mile coming to a junction on the left with the B1343 to Athelstaneford, then soon reaching the summit, where a wide sweep of the Lammermuirs fills the view beyond Haddington. This view has been hidden by the ridge on the climb from Aberlady, the most conspicuous feature then being the Hopetoun Monument (erected in memory of the fourth Earl of Hopetoun in 1824 by "grateful tenantry") just off the B1343 on the ridge's highest point.
On its drop down to Haddington, the A6137 goes over the A1 bypass without a junction then crosses the previous A1 bypass, now the A199, at a roundabout. We now enter the built-up area and fall for a few hundred yards to where the A6137 ends at a crossroads with traffic lights in the town centre. This crossroads used to have the pre-bypass A1 to left and right, now replaced by the A6093 to the left and the B6471 to the right. The fourth arm, ahead, is also the A6093, which has a TOTSO at this point.
For many years, and almost certainly since the A6137 number was first issued to this route, it continued south from Haddington, taking over the former B6368 as far as the A68 near Fala. However, more recently this part of the route has been downgraded once more, and regained its original number - B6368, that number having been maintained for the road connecting the A68 and A7.