Joe Anderson said on Twitter that, despite the best efforts of staff at the Royal Liverpool Hospital’s intensive care unit, his eldest brother died on Friday night.
Thanking “dedicated” hospital workers and the public for messages of support, he called for people to “stick together” amid a surge of coronavirus cases in Merseyside.
The Liverpool City region became the first area to face the toughest local lockdown restrictions in England this week, after being placed on a very high alert level in the new three-tier system.
The mayor tweeted on Saturday morning: “Despite the efforts of all the staff @LivHospitals ICU my brother sadly died at 10.45 last night.
“We want to thank the dedicated staff risking their lives for us.
"Thank you all for your messages of love and support.
"Let’s stick together and support each other and win this battle.”
On Friday evening, Mr Anderson revealed his brother was gravely ill and urged people to follow the rules to prevent the spread of the virus.
“He is in the Royal @LivHospitals in the ICU in a very serious condition,” he wrote on Twitter.
He also highlighted a video shared by the Liverpool City Council Twitter account that featured Dr Richard Wenstone making a plea for people to follow coronavirus rules to ease pressure on the NHS.
Mr Anderson added: “Please watch the video, follow the rules & understand why we all need to fight the enemy #Covid.”