It starts at a mini-roundabout on the B780 by the Auld Kirk in Kilbirnie. The road heads south along Kirkland Road and runs alongside the River Garnock for a short distance before turning east to go over the Ayrshire Coast Line by Glengarnock station.
The road now appears more rural. It continues eastwards through Longbar before crossing the fields to Beith, reaching a roundabout on the A737 bypass. Originally the B777 multiplexed along the A737 into town; now it does the same along the B7049 which has taken on that road's pre-bypass route.
The B777 regains its number in the town centre by turning right into New Street. At the far end is a T-junction where it TOTSOs right into Head Street. It then crosses the A737 bypass at grade, meaning through traffic on the B777 can ignore the detour via Beith town centre. Open country starts on the other side of the A737 and the road continues east across the fields.
After going through Gateside there are no more settlements on the road although it does pass a number of scattered houses. The road runs below the hills to the north, trying to remain flat. Eventually the B775 turns off to the left and the road then skirts the grounds of Caldwell House to end at a T-junction on the A736 to the north of Lugton.