He has made seven appearances in the post-lockdown period and with Luke Shaw injured, is likely to play at left-back in the remainder of United’s Europa League campaign.
“Signing this contract is another really proud moment for myself and my family,” said Williams.
“Having been at Manchester United since I was seven years old, it’s genuinely a dream come true to be playing in the first team. It has taken a huge amount of hard work to reach this point and it has been really special for me to break through into the squad.”
The new deal is reward for what United boss Ole Gunnar Solskjaer said was an “excellent” first season.
“This new deal is a real testament to his hard work and the progress that he has made since his debut,” said Solskjaer.
“Brandon never looked back after stepping up from the academy and, having come all the way through the system, he understands what it means to play for Manchester United.”
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