Blake, 26, crossed the line first in a season's best time of 54.49 seconds to take victory ahead of Roman Pavlyk of the Ukraine.
It means he completes the full set of Paralympic medals after 400m T36 silver and 800m T36 bronze at London 2012.
"I'm lost for words. In 2012 I was fortunate enough to get silver and bronze but I've finally done it and got gold and all the hard work has paid off," he said.
"It's not the ideal lane running from lane eight but I just got on with it.
"I was aware we were on 49 gold medals, it's incredible for us to get so many gold medals and for me to help out with that tally is great."
Paul Blake of Great Britain wins the Gold Medal in the Men's 400m - T36 Final of the Paralympic Game
Image credit: AFP
It is only the third time in British Paralympic history that the team has passed 50 gold medals, and the first since the British Paralympic Association was formed in 1989.
So far gold medals have been won in eight sports, one more than the seven sports, which won gold medals at London 2012.
The team surpassed the 42 gold medals count won in Beijing and, as a result, the team's performance in Rio will be the highest gold medal haul since Seoul in 1988, 28 years ago.
"To reach 50 gold medals is a phenomenal achievement by the whole team. I'm so excited and so proud of the team's performances. I want to congratulate every one of our athletes, as well as all the support teams behind them," said chef de mission Penny Briscoe.
"We came to these Games with a team of 264 of the best prepared athletes that Great Britain has ever produced, ready to take on the best in the world on the greatest stage we have. We know it would be tough, we knew this would be the most competitive Games in Paralympic history, but we were ready for the battle. And the team has excelled.
"We remain focused on the target of 121 set by UK Sport and we know we still have work to do on the field of play in the next couple of days. Our athletes will continue to focus on what they need to do in order to finish the Games in the manner that we have started.
"This Games has been full of outstanding performances and some historic achievements, and there are still several days to go. I can't wait to see what the team will achieve by Sunday."
However, David Weir's nightmare Paralympics continued as confusion reigned in the heats of the 4x400m wheelchair relay. With the top four times progressing across two heats, Rich Chiassaro, Nathan Maguire, Moatez Jomni had put Great Britain in a strong position behind China, who qualified in a world record.
But six-time Paralympic champion Weir appeared to take it easy on the anchor leg, with commentators speculating that he believed the top two in the heat qualified, rather than the fastest four across two heats.
And, in the end, Great Britain missed out on final progress to Canada.
"I went flying round there – I got a higher speed than I did in that 400m heat. I'm just gutted we didn’t qualify," said Chiassaro.