The route starts in the centre of Peel, at a fork junction with the A20 and heads east along Christian Street, forming the northern, outbound, side of a small one way system around the Town Hall. Church Street forms the eastern side, so beyond this junction the A4 becomes two way as it continues to work its way out of town. The older terraced houses that line the start of the route slowly give way to newer properties, with a few blocks of modern infill on Peveril Road, Then after passing a playing field modern housing estates site either side of the road but before long the edge of town is reached, and the route heads out into the countryside. The route has gained a surprising amount of height in the town, but is too far inland for the sea to be visible.
The road then dips down to cross a couple of burns, before climbing again, past a group of houses which stretch as far as the old railway crossing. The small settlement of Knocksharry is at the top of the hill, the roadside thickly lined with trees and hedges, but as it curves around the hillside at Ballanayre, the sea comes into view. Another dip across a burn, and suddenly the road is on the clifftop, with a steep drop into the sea below. On a clear day, Northern Ireland and Galloway are hazy smudges on the horizon, but all too often you are left guessing if it is land or just shapes in the cloud that can be seen. Small fields reappear on the seaward side of the road, and then it turns sharply inland to navigate a horseshoe bend around a steep, narrow gulley. This bend is known as the Devil's Elbow.
The coastal cliffs steadily lose height, and the road drops with them, although always with fields between. The old railway line is re-crossed, and a couple of houses sit on the roadside, but it is the view north along the coast that draws the attention, rugged cliffs hiding bays and coves, and the beaches below. The road dips again to cross Glen Mooar, the climb out less severe than the descent, and then a few more houses appear. Before long, the road is again screened by thick hedges and overhanging trees as it makes a final descent into Glen Wyllin, beyond which lies Kirk Michael. The A4 comes to an end at a forked T junction on the A3 at the entrance to the village.
The A4 originally ran from Castletown to Kirk Michael, with the A3 running from Peel to Ramsey. At some point before 1987 the A4 was possibly extended from Kirk Michael along the A3 to Ramsey, although this may just be a mapping error. In 1987 the numbers were swapped, putting the A3 and A4 on their current routes.