The Mulranny-Achill section is a 13km long trail. In Mulranny an official access point is located to the right just off the N59 travelling to Bangor. An access point is also located at the old Mulranny Railway Station behind Mulranny Park Hotel.

At Achill Sound an official access point is located at Óstán Oileán Acla / Achill Island Hotel at the gateway to Achill Island. Follow finger post signage onto Greenway.

The estimated time is 1-1.5 hours for cycling and 2-2.5 hours for walking.

The track winds along the North side of Clew Bay and commands spectacular views of Croagh Patrick on the other side of the bay.

This section passes through very distinctive habitats such as salt marshes, Rossmurrevagh machair around Mulranny and several Special Areas of Conservation. Machair is a unique type of sand dune habitat found only in the West coast of Ireland and Scotland and it is one of the rarest wildlife habitats in Europe.

Here the Great Western Greenway runs through woodland in the shadow of Claggan Mountain and opens onto Bellacragher Bay where mussels rafts can be seen in the clear waters. It crosses streams such as Cuillaloughan River, Glennanean River and Cartron River.

It passes by small lakes such as the lovely Lough Gall where stacks of turf can be seen to dry near the shore. This area is protected and is part of the Lough Gall Bog SAC.

Cycling this section many species of fauna and flora can be spotted including feral goats, Black Faced Sheep and Ling Heather.

At the end of the section coming closer to Achill Island, Slievemore comes in sight. Here the trail offers spectacular view of Blacksod Bay, Annagh Island and Inishbiggle.