"Patient 1145", 29, arrived at Van Don International Airport in the northern Quang Ninh Province on Tuesday on Vietnam Airlines flight VN8.
Upon entry, he was sent to quarantine at a military facility in Bac Ninh Province, also in northern Vietnam.
His test result came back as positive with the coronavirus the next day. He is now treated at Bac Ninh General Hospital.
A woman and her eight-month-old son who returned from Angola on the same flight were confirmed Covid-19 patients on Wednesday evening.
The nation's Covid-19 tally now stands at 1,145, among which 1,046 have recovered and 35 have died with the disease.
In all cases registered in the country, 691 are community transmissions and the rest are foreigners or Vietnamese citizens coming or returning from abroad.
By Thursday, Vietnam has gone 49 days without recording any new community transmission. It is putting almost 14,000 in isolation, including 150 at hospitals, 12,000 in centralized facilities, and the rest at home or other accommodation facilities.
Over 1.1 million people have died of Covid-19 worldwide. The U.S., India and Brazil are the three most infected countries.