Born and raised on a farm outside Melbourne, Victoria, George Coulthard helped lead the Carlton Football Club to premiership success in the fledgling Victorian Football Association (VFA), and was a key member of the Victorian side that dominated the first intercolonial matches. A fast, versatile and highly skilled footballer, Coulthard was, in the opinion of many of his contemporaries, the greatest player yet seen in the Australian game. However, his football career ended in controversy in 1882 when he received a season-long suspension - then the most severe punishment ever handed down by the VFA - for brawling and using "bad language" during play. A colourful character and admired widely for his exceptional sporting prowess it would seem George Coulthard had the world at his feet before fate stepped in.

In March 1879, Coulthard spied on and captured William Grieves, a notorious criminal who had eluded detection for five years, and delivered him into police custody. Coulthard was later reportedly admitted as a member of the Victoria detective force. Coulthard also donated a koala to the precursor of the Melbourne Zoo in 1880.

As a professional cricketer, he played at club level for Melbourne, represented Victoria in five first-class intercolonial matches, and made one Test appearance for Australia, against England in 1882. Coulthard also umpired one of the earliest Tests at age 22, and although he remains the youngest ever Test umpire, he is perhaps best known in cricket for instigating the sport's first international riot when, in 1879 in Sydney, he controversially gave New South Wales batsman Billy Murdoch out against Lord Harris's English XI. Coulthard was co-officiating the match with Edmund Barton, later the first prime minister of Australia.

Coulthard's sporting exploits made him a household name throughout Australia. Off the field, he ran a tobacco and sporting goods store in Lygon Street, Carlton, and won additional fame for surviving a shark attack off Shark Island, fighting bare-knuckle boxing champion Jem "The Gypsy" Mace, and being the alleged source of a dream premonition that convinced many Melbourne Cup punters to back a horse with long odds (the horse finished close to last). Coulthard is also known as Australian football's first "man in white" for umpiring an 1880 match in the now-traditional all-white uniform. In 1882, while serving as the England cricket team's umpire on its first quest to regain The Ashes, Coulthard became ill with tuberculosis, from which he died the following year, aged 27. However, George packed plenty into his short life and became a cult hero, both loved and loathed.

Carlton was the powerhouse of Victorian football in the early years.[Starting off as one of Carlton's followers, he was described by The Footballer as a "rising and most promising player.” The Victorian Football Association (VFA) was established the following year, with Carlton as one of its twelve foundation member clubs. Despite switching between attacking and defensive positions during the 1877 VFA season, Coulthard still managed to rank equal-first on Carlton's goal-kicking tally with eight goals, and his elusive dashes with the ball in hand, fully 100 metres up the field at times.

In 1877, against Melbourne, Carlton was already acknowledged as having won the premiership - its fifth such honour in seven years - based on the results of previous encounters between the two clubs that season. Coulthard was instrumental in maintaining Carlton's supremacy and was voted by The Australasian in its end-of-season review as one of the VFA's best backline players. At the Melbourne Cricket Ground (MCG) the following month, in the first club football match staged at night under electric lights, Carlton triumphed over Melbourne 3–0, two of the goals coming from Coulthard. He ended 1879 with a record 21 goals, seven more than the runner-up.

In 1882 the VFA held a special meeting at the Young & Jackson hotel regarding a violent on-field incident involving George Coulthard and Joey Tankard. They ruled Coulthard was "more to blame" for the fracas, with chairman Mr C.A Harrison expressing the opinion that "bad language is far worse than blows." Both players received a season-long suspension - the first punishment of its kind carried out by the association. He never played senior-level football again.

Coulthard began his cricket career at the Carlton Cricket Club. For the 1877/78 season, he transferred to the Melbourne Cricket Club (MCC), which took him on as a professional ground bowler (a job that involved bowling to members in the nets). In 1878/79, he went in as a substitute for a Victorian XV during a match against the first representative Australian team, and batted in the lower order for the MCC when it hosted New Zealand's visiting Canterbury XI.

Coulthard was only 22 when Lord Harris, captain of the touring England XI, put him on trial as the team's umpire on the advice of the MCC. Coulthard officiated the team's first match in Melbourne, against a Victorian XV, on Boxing Day 1878, and fulfilled the same duty in the lone Test match of the tour, against Australia, held at the MCG on 2–4 January 1879. Satisfied with Coulthard's umpiring, Harris invited him to accompany the team and stand in as umpire for the remainder of the tour.

The England team's next first-class match was against New South Wales on the Association Ground in Sydney - Moore Park. As a hired professional, Coulthard was viewed with suspicion by many Sydneysiders and, in an era of intense rivalry between the colonies, the fact that he was a Victorian only deepened their distrust. Even so, New South Wales was tipped to win based on England's losses in Victoria, and illegal gamblers had placed heavy bets in favour of the home side. The first game passed off without incident, New South Wales winning by five wickets.

England fought back in the return match, which began on 7 February. In reply to the tourists' first innings total of 267, Billy Murdoch, the star of New South Wales, carried his bat for 82 out of 177 runs and had reached 10 in the follow-on when Coulthard gave him run out. The dismissal caused an uproar in the crowd of 10,000, incited, it was alleged, by bookmakers and their cohorts in the pavilion, who told Murdoch to stay on the field. It was not Coulthard's first controversial call; on the first day, he gave the caught Harris a second life, a "blatant error" according to one match reporter.

Ignoring his team's umpire Edmund Barton, who deemed the run out fair, NSW captain Dave Gregory threatened to abandon the match unless Harris had Coulthard replaced. While the captains conferred, one of the English fieldsmen inflamed the situation by addressing hecklers in the crowd as "nothing but 'sons of convicts'". At this point, up to 2,000 "roughs and larrikins" surged onto the pitch. Some of the England players armed themselves with stumps as defensive weapons. Harris, in defending Coulthard, was struck with a heavy stick, and A. N. "Monkey" Hornby collared and dragged the assailant to the pavilion, taking punches and nearly losing his shirt in the process. Powerless to restore order, the mounted police were able to rescue Coulthard only after a lengthy struggle and with the help of volunteers.

Harris agreed to continue the match after Sunday break on the condition that Coulthard stood in as umpire. England won by an innings and 41 runs, and then cancelled its remaining fixtures in Sydney. The riot was reported on widely as a national disgrace and a blow to Anglo-Australian relations. The Sydney press maintained that Coulthard was either incompetent or "wilfully corrupt" as umpire.

It was late in 1891 that Fred Spofforth was to clarify the situation regarding the inter-colonial rivalry in his statement:

“I should like to point out that the feeling aroused was almost entirely due to the spirit of the rivalry between the Colonies ... The umpire was Victorian, and the party spirit in the crowd was too strong, ‘Let an Englishman stand umpire,’ they cried; ‘we don't mind any of them. We won't have a Victorian.’

The Evening News (Sydney) on Feb 10, 1879, needless to state, offered a somewhat brash and forthright opinion:

“Melbourne larrikins do not make good umpires. The ups and downs of colonial life are great. A Lord may any day be yoked to a larrikin.”

Coulthard was brought into a Victoria XV in March 1880 to take on that season's Australian representative team. He was the leading wicket-taker for his side with 5/52 and 4/28. In his first-class debut for Victoria later that year, against South Australia on the East Melbourne Cricket Ground, he took 3/29 and contributed 31 runs to a first innings total of 329, but his performance with the leather slumped in the second innings, conceding 49 runs for a single wicket. The following month, after top scoring (51) for a Victorian XV in a match against the Australian XI, Coulthard played in his first of three first-class contests against New South Wales. He failed to make much of a statistical impact for Victoria in any of these intercolonials.

Given the inconsistency of his first-class outings, it is considered an oddity that, during the 1881/82 season, Coulthard, then Victoria's twelfth man, was selected to play for Australia against Alfred Shaw's touring England team following the withdrawal through injury of Alick Bannerman and Fred Spofforth. Batting at number eleven, he scored 6 not out in a useful last wicket stand of 29 with fellow Test debutant Sammy Jones. It would be Coulthard's solitary Test appearance, earning him the rare distinction shared only with fellow Australian Paddy McShane of playing in a Test after umpiring in one. Also, by a "twist of fate", his captain in the match was Billy Murdoch.

In November 1882, Coulthard was appointed umpire for Ivo Bligh's touring England XI on its famous quest to recover The Ashes. Coulthard fell ill during a sea voyage early on in the tour, and on the second day of a match in Newcastle, suffered "severe indisposition" and retired from his post. Coulthard had contracted tuberculosis, and he was feared to be on the verge of death by the start of the 1883 VFA season. News of his death at 223 Lygon Street in Carlton, Victoria on 22 October was met with an outpouring of public grief, and a large procession followed Coulthard's remains from his Lygon Street home to his funeral. He was buried at the Melbourne General Cemetery next to Princes Park, home of the Carlton Football Club.

Coulthard earned a place in the annals of Australian horse racing for a dream he reportedly had in the weeks before his death. The story went that Coulthard, lying on his deathbed, dreamt that Martini-Henry would win the Victoria Derby, Dirk Hatteraick the Melbourne Cup, and that he himself would die before the first-named race was run. Coulthard's dream was "the great topic of the day" and received significant media coverage. When he died before Martini-Henry won the Derby, a "rush of superstitious punters" placed bets on Dirk Hatteraick to win the Cup, causing a sharp drop in odds, despite the fact that, in the words of one turf writer, the horse was "as fat as a bacon hog". Dirk Hatteraick finished in the tail end of the field.

Coulthard was inducted into the Carlton Football Club Hall of fame in 1990, and is one of the few players of his generation to be a member of the Australian Football Hall of Fame. Coulthard is depicted in the MCG Tapestry, designed by artist Robert Ingpen and unveiled at the MCG in 2003 to commemorate the ground's 150th anniversary.