In contrast to Donald Trump who has not worn masks during public appearances, both Mr Biden and his wife Jill Biden wore black face masks to lay a wreath a memorial for World War II and Korean War veterans in Delaware.
Mr Trump and Melania Trump didn't wear masks during a Memorial Day ceremony at Baltimore's Fort McHenry or while laying a wreath earlier at Arlington National Cemetery in Virginia.
Mr and Ms Biden were flanked by full Secret Service protection as they laid a wreath of white flowers tied with a white bow before bowing their heads in silence at the Memorial Bridge Veteran's Memorial Park.
"It feels good to be out of my house," Biden told reporters before saluting about a dozen veterans from a distance and thanking them for their service.
It was the first time the presumptive presidential nominee has campaigned outside his Wilmington home since the start of the coronavirus lockdowns.
"Never forget the sacrifices that these men and women made," Mr Biden said. "Never, ever, forget."
Since the cancellation of a rally in Cleveland on 10 March, Mr Biden has done most of his campaigning appearing virtually on news programmes, talk shows, and social media platforms.
While the president has travelled to states like Arizona and Michigan, he criticised Mr Biden's stay-at-home campaigning.
"I'd love to see him get out of the basement so he can speak," Mr Trump said in a telephone interview with Fox News.
Mr Biden criticised Mr Trump for playing golf over the weekend, with his campaign releasing a video of Trump at his Virginia course saying "The death toll is still rising. The president is playing golf."
"The presidency is about a lot more than tweeting from your golf cart," Mr Biden posted on Twitter on Sunday.
The presidency is about a lot more than tweeting from your golf cart. It requires taking on the ultimate responsibility for the biggest decisions in the world. Donald Trump simply wasn't prepared for that. I promise you I will be.
— Joe Biden (@JoeBiden)
Mr Trump's Memorial Day plans included a visit to the Arlington National Cemetery and the Fort McHenry national monument in Baltimore, despite pleas from the city's mayor to stay at home and not bring the presidential entourage to Democrat stronghold.