Douglas Lambert was born on 4 October 1883 in Cranbrook. He went to school at St Edward's in Oxford and then Eastbourne College.

Lambert, who was big, strong and fast, played for Harlequins A XV until he was selected to play wing for the first team in 1905. Being large, he joined as a forward. Adrian Stoop, who had been selected for Harlequins in 1901 while still at school at Rugby, was appointed club secretary in 1905 and was captain the following year. He brought about a transformation at the club, attracting exceptional back line players such as John Birkett, Ronnie Poulton, Herbert Sibree and Lambert: Harlequins became the leading club in England. It was Stoop who brought Lambert into the first team as a threequarter after Lambert had demonstrated his speed and strength by tackling Stoop in practice. After his first season with the first team, Lambert was invited on the Barbarians' Easter tour of Wales in 1906, but he was on the losing side in the three matches in which he played, against Penarth, Cardiff and Plymouth.

Lambert's debut for England was against France in January 1907. Selected to play on the wing only after the original choice had pulled out, Lambert scored five tries, a record for any nation, which stood until Marc Ellis scored six tries for New Zealand against Japan in the 1995 Rugby World Cup. Lambert was subsequently dropped from the England team until the following year. In the meantime, he continued to play for Harlequins and was again invited to tour with the Barbarians, winning two of the three matches.

He was brought back to the England team in 1908 to play in the fixture against France, and scored another try. He also played in the 1908 season's games against Wales and Scotland but was not selected again until 1911, when he played his final three international matches. After playing against Wales, he went on to score another two tries, five conversions and two penalties in the next game, England's first against France at its new home ground of Twickenham: the 22 points were a record for England that stood until 1990 when Simon Hodgkinson scored 23 points against Argentina. Four of the England backline that day were Harlequins players: Birkett, who captained England, Stoop and his brother Freek, and Lambert. Lambert's final match was against Ireland at Lansdowne Road.

At the outbreak of the First World War, Lambert was commissioned second lieutenant in the 6th Battalion of The Buffs (East Kent Regiment). Before departing for France in December 1914, he was married to Joyce, his childhood girlfriend, and she fell pregnant. His battalion took part in the Battle of Loos in September 1915. On 13 October, in an attempt to break through German lines, The Buffs were decimated, losing 400 men in just a few minutes, Lambert amongst them. Two months after his death, his son was born.