The top seeds were far too strong for their compatriots and second seeds Xu Chen and Ma Jin as they powered to a 21-11 21-17 victory at Wembley Arena.
The bronze medal was won earlier in the day by Danish pair Joachim Fischer and Christinna Pedersen, who beat Indonesia's Tonowi Ahmad and Liliyana Natsir.
The result of the gold encounter rarely seemed in doubt after world champions Zhang and Zhao got off to a superb start, racing into a 12-5 lead.
Zhao, despite apparent trouble from a knee injury, rarely relinquished control at the net while Zhang set up plenty of winners.
Their opponents could not impose themselves and were frequently forced into errors.
Zhang and Zhao led 8-0 in the second game and only had a brief struggle two points from victory as Xu and Ma won four in succession.
But victory was not long delayed and Zhang ran to the crowd to collect a flag from a supporter and threw his shoes into the audience.
Fourth seeds Fischer and Pedersen earned some consolation after their semi-final defeat by outplaying third seeds Ahmad and Natsir to win 21-12 21-12.
The result meant that for the first time in Olympic Games history Indonesia had failed to pick up a Badminton medal. At all previous Games since the sport was introduced at Barcelona 1992, the country had won at least one gold.
Ahmad said: 'I failed to cope with the expectation and under-performed.'
The men's Singles final on Sunday will be a repeat of the Beijing 2008 showpiece of four years ago between all-time greats and arch-rivals Lee Chong Wei and Lin Dan.
Defending champion Lin had little trouble seeing off Republic of Korea's Lee Hyun-il.
The world number two won 11 of the first 12 points of the match and 12 of the last 14 as he powered past seventh seed to win 21-12 21-10.
Malaysia's top seed Lee was made to work much harder by third seed Chen Long and looked more impressive for it as he won 21-13 21-14.
Lee and Lin produced a stunning spectacle when they met in the final of the World Championships at the same venue last year.
Lin survived match point to win and will again be favourite, despite Lee's long-established status at the top of the world rankings.
The Malaysian, a perennial runner-up to Lin, will also carry the pressure of bidding to win his country's first Olympic Games gold in any sport.
The first women's semi-final proved a disappointing spectacle as top seed Wang Yihan made easy work of India's fourth seed Saina Newhal, winning 21-13 21-13 in 42 minutes.
Wang was joined in the final by fellow Chinese Li Xuerui, who beat another compatriot in Wang Xin.
Third seed Li, a late selection by China for the tournament, continued her impressive progress with a 22-20 21-18 success over the second seed.