On 10 May, despite an absence of 9+1⁄2 months he started favourite for the Poule d'Essai des Poulains over 1600 metres at Longchamp Racecourse but finished sixth of the eighteen runners behind Make Believe.

After being hampered in the early stages, Highland Reel settled in fourth place before moving forward in the straight, taking the lead inside the final furlong and winning by 1+1⁄2 lengths from Scottish.

In a race run in heavy rain, Highland Reel went to the front from the start, set a steady pace, accelerated on the final turn and drew away to win by five and a quarter lengths from Closing Bell.

[10] On his return to Europe he started the 16/1 outsider in an exceptionally strong seven-runner field for the Irish Champion Stakes and finished fifth behind Golden Horn, Found, Free Eagle and Pleascach.

Highland Reel's travels continued in October when he was shipped to Australia to contest the Cox Plate over 2000 metres at Moonee Valley Racecourse, a race which his stable had won with Adelaide in 2014.

On his final appearance of the season the colt ran in the Hong Kong Vase at Sha Tin Racecourse and started the 5/1 second favourite behind Flintshire.

"[12] Highland Reel began his third season with a journey to the United Arab Emirates for the Dubai Sheema Classic on 26 March and finished fourth behind Postponed, Duramente and Last Impact.

He was back in Hong Kong in April for the Queen Elizabeth II Cup but met trouble in running and finished eighth behind Werther.

On 23 July, over the same course and distance, Highland Reel faced a rematch with Dartmouth in Britain's most prestigious weight-for-age race, the King George VI and Queen Elizabeth Stakes.

Ridden by Heffernan, he was among the leaders from the start and stayed on well in the straight to finish second behind the favourite with The Grey Gatsby, Hawkbill and Wings of Desire unplaced.

On 5 November at Santa Anita Park Highland Reel, ridden by Heffernan, started third favourite behind Flintshire and Found for the $4 million Breeders' Cup Turf.

Breaking quickly from an outside draw, Highland Reel took the lead soon after the start and set a steady pace before kicking seven lengths clear of his opponents at half way.

[15] After the race Aidan O'Brien said "We knew that he gets a mile-and-a-half well, that he handles fast ground and doesn’t mind dictating, so it was straightforward really, but Seamus executed it brilliantly.

[16] As in the previous year, Highland Reel ended his season with a run in the Hong Kong Vase and started the 1/2 favourite to repeat his 2015 success.

Ridden by Moore, he went to the front from the start, regained the advantage after being headed by the British-trained Big Orange, and galloped three lengths clear of his rivals in the straight.

"[18] On his next appearance Highland Reel was dropped back to ten furlongs for a rematch with Jack Hobbs in the Prince of Wales's Stakes at Royal Ascot.