Within months he had progressed to the first eleven, seeing his club keep its league status and to the Scottish Cup semi-final in 1928. In the meantime he had In 1927 and still a teenager won the first of his twelve caps over six seasons. And it was the combination of Cup and Wembley success that saw him finally in May 1928 take the professional shilling, joining Hearts, where at Tynecastle for the rest of his career and over three hundred games he remained but actually with, first, little team-success, second, towards the end knee injuries and finally on his part perhaps waning interest. In fact in 1936 he was to lose his First Team place and, whilst hanging on for the rest of the season, it was to prove the catalyst  for retirement at its end aged just twenty-nine. 

But then it was also in 1936 that he was married, to Isabella Smith, interestingly with his employment recorded not as footballer, nor yet journalist but "Brewers' Representative". They were to have one son. However,  journalism, specifically sports journalism, was after service during the War to be Jack Harkness's future. He was to become the honoured doyen of the profession in Scotland. His column in The Sunday Post was simply labelled "Jack Harkness Here". And it, on top of his playing career, saw him in 1971 before final retirement awarded the MBE. 

John Diamond Harkness would die in Newlands, in south Glasgow, a mile from where he had grown up. The year was 1985, he aged 78. And he was cremated at Linn Park in Cathcart, again no more than a mile from his homes both in youth and old-age.