Unraced as a two-year-old he showed steady improvement in 2016, winning two minor races and finishing second in the Queen's Vase before recording a 22/1 upset victory in the St Leger.

[3] Harbour Law's dam Abunai showed some ability as a racehorse, winning three times as a two-year-old in 2006,[4] and was a granddaughter of the Child Stakes winner Inchmurrin.

[6] Eighteen days after his win at Salisbury Harbour Law was moved up in distance for a handicap over fourteen furlongs at Sandown Park Racecourse in which he was allotted top weight of 133 pounds.

After taking the lead approaching the last quarter mile he was overtaken in the closing stages and finished fourth of the nine runners behind the Aidan O'Brien-trained Housesofparliament.

[8] On 10 September Harbour Law, partnered by Baker started a 22/1 outsider in a nine-runner field for the 240th running of the St Leger Stakes over 14+1⁄2 furlongs at Doncaster Racecourse.

Idaho started the odds-on favourite whilst the other runners included Sword Fighter, Housesofparliament, Ventura Storm (Prix de Reux) and the John Gosden-trained Muntahaa.

Housesofparliament and Ventura Storm appeared to have the race between them but Harbour Law produced a strong late run to gain the advantage in the final strides and won by three quarters of a length.

On 22 June 2017 at the same track Harbour Law was partnered by Jim Crowley when he went off a 33/1 outsider for the Group 1 Ascot Gold Cup over two and half miles ran.