Martin arrived back on the Isle of Man in July in order to compete in the Southern 100 Races which were celebrating their Diamond Jubilee. Poor weather initially hampered the racing programme with the Corlett's Trophies 1000/600cc race red flagged in wet conditions.[39] The race was re-run two days later, with Dan Kneen taking the lead for the opening two laps. However, Martin edged him out, taking the lead on lap 3 and thereafter dicing for the lead with Kneen and Michael Dunlop.[40] Leading at Stadium Corner on the final circuit, Martin looked favourite to take the honours. However, getting maximum drive out of the final corner, Dunlop snatched victory at the line by 0.087 seconds.[41]
Martin then began to take hold of the meeting. Onboard his BMW S1000RR Martin took to the grid for the finale to the event, the Southern 100 Solo Championship.[42] Pushed hard during the 9 lap race by Dan Kneen, Martin led the pack by the end of the opening lap and continued to hold station at the end of lap 2. Lap 3 saw Martin maintain his lead, however Dunlop low sided at Ballabeg Hairpin putting him out of the race.[43] The ensuing melee enabled Martin and Kneen to break free from the chasing pack and their two-way battle ensued into the following lap.[44] As the race went into the final two laps, the rear echelon of the field started to have an effect on the front running riders, with Kneen being held up in an overtaking manoeuvre at Iron Gate.[45] This enabled Martin to stay clear on the final circuit taking the Southern 100 title for the third year in succession.[46]
Martin at Church Bends during the 2015 Southern 100.
Following his victory, Guy Martin joined the late Joey Dunlop as the only riders to of won the Southern 100 Solo Championship Race for three years in succession.