The former vice-president was quick to offer "prayers" to the president and the first lady after both contracted coronavirus.
He was speaking shortly before it was announced Mr Trump would be taken to a military hospital where we will remain for a “few days” on the advice of doctors.
He stressed: "This is not a matter of politics, it's a bracing reminder to all of us that we have to take this virus seriously".
While offering good wishes to the Trumps, Mr Biden did deliver some thinly veiled critiques of the president's actions during the pandemic.
"We have to do our part to be responsible, it means following the science, listening to the experts, washing our hands, social distancing, it means wearing a mask in public and it means encouraging others to do so as well."
Since the virus emerged at the start of the year the president, the White House and his campaign have played down the threat and been reluctant to abide by public health guidelines - including mask wearing.
Delivering his speech with a mask on throughout, Mr Biden - who has twice tested negative since news of the president's diagnosis broke - encouraged other Americans to wear masks.
"Be patriotic, it's not about being a tough guy, it's about doing your part," he said.
"Wearing a mask is not only going to protect you, but it also protects those around you. Your mum, your dad, your brother, your sister, husband, wife, neighbour, co-worker.
"Don't just do it for yourself - do it for the people you love".
The issue of masks became political for a time for many Americans, as president Trump refused to appear in public wearing a face covering for many months.
Mr Trump first wore a mask in public in July.
The president has at times accused press reporters of wearing them to be politically correct and has retweeted messages making fun of Democrat Joe Biden for wearing a mask and implying that Mr Biden looks weak.
Donald Trump's positive diagnosis comes just a month before the US election on November 3.