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.