Teenage wunderkind Smith rewarded by Harlequins
The 18-year-old Philippines-born flyhalf – whose father is English and mother Filipina – has made such an impression he was called up by England head coach Eddie Jones for last November's Tests.
This came on the back of performances such as being the man of the match in Harlequins defeat of Wasps – only a fortnight after making his senior debut – ending the latter's 22 game winning home streak.
"I'm delighted to have secured Marcus' long-term future at Harlequins," said Harlequins Director of Rugby John Kingston.
"Marcus is an intelligent and humble young lad who is very focused on his rugby.
"He has the talent and abilities to take this Quins side forward onto the next stage of its development.
"He is the type of player and person that perfectly embodies the Harlequins spirit and culture we are building."
Smith, who has played for England at Under-16 and 18 levels, said thanks to the spirit at Harlequins he had flourished.
"Harlequins is a fantastic club and they have looked after me extremely well since I joined three years ago," said Smith.
"The club is incredibly ambitious and combined with John Kingston’s long-term vision, it made the decision much easier knowing the faith and guidance he has shown me."
Agence France-Presse
