Welby, 69, will be replaced on a temporary basis by outgoing Archbishop of York Stephen Cottrell, currently the second most senior cleric in the mother church of Anglicanism.
He has also faced calls to resign over his own handling of a historical sexual abuse case.
The process to choose Welby's permanent successor is set to take several more months and not be announced until later in the year, according to reports.
Welby, who resigned in November, is expected to spend his final day in the post privately at his London base of Lambeth Palace, UK media said.
He will attend two services there -- a Eucharist at lunchtime and Evensong later in the day -- before his 12-year-tenure formally ends at midnight (0000 GMT), the reports added.
He is set to lay down his bishop's crozier -- a ceremonial long staff -- in a symbolic act marking the official end of his time as Archbishop of Canterbury, they noted.
'Tone deaf'
Welby quit after an independent probe found that he "could and should" have formally reported decades of abuse by Church-linked lawyer John Smyth to authorities in 2013.
Smyth, who organised evangelical summer camps in the 1970s and 1980s, was responsible for "prolific, brutal and horrific" abuse of as many as 130 boys and young men, according to the independent Makin Review.
It concluded the Church of England covered up the "traumatic physical, sexual, psychological and spiritual attacks", which occurred in Britain, Zimbabwe and South Africa over several decades.
Smyth, who lived in Africa from 1984, died there aged 75 in 2018 while under investigation by British police. He never faced any criminal charges.
Welby has made few public appearances in the wake of his resignation and did not give the traditional Christmas Day sermon from Canterbury Cathedral.
A House of Lords peer through the Archbishop of Canterbury post, he had to apologise in late November over his final speech in parliament's upper, unelected chamber.
Critics accused him of appearing "tone deaf" after his remarks referenced a 14th-century beheading and prompted laughter from some other peers.
'Deeply sorry'
Cottrell, who became Archbishop of York in 2020, steps up to temporarily replace Welby while also tainted by scandal.
The 66-year-old faced calls to stand down last month over claims he too mishandled a sexual abuse case during his time as the Bishop of Chelmsford, in southeastern England.
Priest David Tudor remained in his post despite Cottrell knowing that the Church had banned him from being alone with children and had paid compensation to a sexual abuse claimant, the BBC reported.
Cottrell has said he is "deeply sorry that we were not able to take action earlier" but defended his actions.
A bishop for 15 years -- first in Reading and then Chelmsford -- Cottrell briefly worked in the film industry before training for the priesthood. He was ordained aged 25.
He has ruled himself out of being Welby's permanent successor, saying the Church -- which requires bishops to retire at 70 -- needs a younger long-term leader.
"We need someone who can give at least five years, probably more like 10. So I don’t consider myself to be a candidate," he said in November.
The Anglican Church is the established state Church in England and dates back to Henry VIII's split from the Roman Catholic Church in the 1530s.
King Charles III, its supreme governor, appoints archbishops on the advice of the prime minister.
