The program, which will roll out in coming months, will be open to an estimated 500,000 spouses who have lived in the US for at least 10 years as of June 17, senior Biden administration officials said in a call with reporters.
Some 50,000 children under age 21 with a US-citizen parent also will be eligible, they said. The majority of people who would likely benefit are Mexicans, they added.
The program will allow the spouses and children to apply for permanent residence without leaving the US, removing a potentially lengthy process and family separation. They could eventually apply for US citizenship.
Biden, a Democrat seeking a second term in the White House, took office vowing to reverse many restrictive immigration policies of Trump, who is also seeking a second term in the White House. But faced with record levels of migrant arrests at the US-Mexico border, Biden has toughened his approach in recent months.
Earlier this month, Biden barred most migrants crossing the US-Mexico border from requesting asylum, a policy that mirrored a similar Trump-era asylum ban.
Biden's planned legalisation program for spouses of US citizens could reinforce his campaign message that he supports a more humane immigration system and show how he differs from Trump, who has long had a hardline stance on both legal and illegal immigration.
Biden is expected to make the announcement at a White House event on Tuesday tied to the anniversary of the Deferred Action for Childhood Arrivals program.
The DACA program was launched in 2012 by former president Barack Obama and then-vice president Biden and currently grants deportation relief and work permits to 528,000 people brought to the US as children.
The Biden administration also is expected on Tuesday to roll out guidance that could make it easier for DACA recipients to obtain skilled-work visas.
US Representative Adriano Espaillat, a Democrat attending Tuesday's event, said the relief for spouses is a way for the administration to balance out recent border enforcement measures.
Trump campaign spokesperson Karoline Leavitt called Biden's new program "amnesty" in a statement and reiterated Trump's deportation pledge, saying he would "restore the rule of law" if re-elected.
A little more than half of US voters back deporting all or most immigrants in the US illegally, Reuters/Ipsos polling shows.
