Jenkins was educated at Edinburgh Academy, where he excelled at sport. He started off as Scottish 100/200/400 Champion, followed by his first of 6 AAA's 400metre titles. Also In 1971, still aged only nineteen, Jenkins won the 400 meters at the European Athletics Championships in Helsinki
In 1975 he was United States of America 400 metre champion, with his fastest time of his career 44.93 which was a British record at the time.
In 1978 he won a gold medal competing for Scotland at the Commonwealth Games in Edmonton, Canada in the 4 x 100 m relay, alongside Cameron Sharp, Allan Wells and Drew McMaster.