The 30 year old from Hereford had been in a coma since the bombings on 7July and finally lost his fight for survival on Saturday.
It has been confirmed that his girlfriend of 13 years, 36-year-old Samantha Badham, has also died.
It is understood the pair were caught up in the King's Cross Underground blast, which has so far claimed 27 lives.
The couple, who were due to celebrate their 14th anniversary just two days after the attacks, had only caught the Tube that morning because they had planned to go for a romantic meal. They usually preferred to drive or cycle into work.
Harris moved to London to study architecture at the University of North London and spent his year out working at Geoffrey Reid Associates.
After completing his Part 2 examinations at the Bartlett School of Architecture, he returned to the practice which had been renamed Reid Architecture.
His first project was an office development in Maidenhead and he was soon involved in the high-profile Three Quays next to the Tower Of London.
More recently he had led the design team on proposals for Southampton airport.
In a statement released today, the practice paid tribute to his 'generous spirit' and to his 'dedication, tenacity and meticulous determination for getting it right'.
Andrew Leckenby, a director with the company, said: 'During lectures, design reviews and the informal discussion that drives an architectural studio he was always present to contribute his knowledge and intellect.
'He also enriched the culture of the working environment through his contributions to staff art shows, in particular with his highly individual and thought-provoking light installations, which brought life to the office gallery.'
He added: 'But it is not just for his design work that Lee will be remembered. In his trademark white T-shirt, his ever present smile, calm confidence and generous spirit were, and will remain, an inspiration to everyone on the office.'