The new UKIP leader will be announced at the party's annual conference in Bournemouth shortly.
Five contenders stood for election after Nigel Farage resigned in July, saying the UK's Brexit vote meant his political ambition had been achieved.
A ballot of party members closed on Thursday and the result will be announced at 13:30 BST on Friday.
The candidates are MEPs Diane James and Bill Etheridge, councillor Lisa Duffy and Liz Jones and Phillip Broughton.
The race to succeed Mr Farage has proved controversial with two leading candidates barred from standing and another pulling out of the contest.
In August, the man widely regarded as the favourite to win, Steven Woolfe, was ruled ineligible by the party after missing a deadline to submit his papers online. Suzanne Evans had already been excluded due to her suspension from the party.
Later that month, Jonathan Arnott withdrew, saying the best he could hope for would be to come second.
Mr Farage told BBC Breakfast he was not endorsing any of the candidates and pledged to give the winner his full support and let them get on with running the party.
"Following on from me won't be easy because I have been quite a dominant figure - some people like that and some don't. So whoever wins wins.
"I am stepping down as leader and stepping back from the front line. I still support everything UKIP stands for and I will support whoever wins."
As to his own future, Mr Farage said he would remain as an MEP and continue to press for the government to secure a deal for leaving the EU that fulfilled the public's expectations on immigration and other issues.
He added: "I am not retiring. I am not moving to a flint cottage in Snowdonia never to be seen again."
In 2009, Mr Farage stepped down as leader to be replaced by Lord Pearson. However, he returned less than 18 months later to take charge after the 2010 general election.
Who are the five contenders?
Phillip Broughton was a Conservative councillor from 2007 to 2011 before defecting to UKIP.
He stood for election to Parliament in Hartlepool at the 2015 general election, narrowly losing to incumbent Labour MP Iain Wright, who retained the seat with a majority of 3,024 - down from 5,509.
He says UKIP has "won the arguments" on Brexit and now needs to "broaden our message" - on the economy, NHS, defence, law and order, foreign policy and foreign aid.
He describes himself as a "young, passionate, northern, working-class guy", is a semi-professional wrestler and works as a supervisor in a local Tesco.
Lisa Duffy is is a town and district councillor in Cambridgeshire, a former mayor of Ramsey, and has been a campaigns director during by-elections.
Little-known in Westminster, she won the backing of key modernising figures in the party such as Suzanne Evans and Patrick O'Flynn.
She joined UKIP in 2004, is chief of staff to MEP Mr O'Flynn and stood unsuccessfully against Labour's Hazel Blears in Salford in the 2005 general election.
The mother of six and former retail manager pitched herself as a "grassroots candidate" who would "walk the People's Army into Westminster".
A former Conservative activist, now an MEP for the West Midlands and Dudley councillor, Mr Etheridge wants UKIP to stick to its "core principles and values".
He has called for major reform of the penal system, including restricting prisoners' privileges, banning visits during the first six months of a sentence and an automatic 10-year increase in sentence for anyone attacking a prison officer.
He backs far-reaching changes to the tax system - including a 50% cut in alcohol and tobacco duty, replacing VAT with a local sales tax and gradually merging National Insurance and income taxes.
Diane James lost the 2013 Eastleigh by-election to the Liberal Democrats by fewer than 2,000 votes, relegating the Conservatives into third place.
She was elected to the European Parliament as MEP for South East England in 2014, and decided against standing in the 2015 general election for personal reasons.
A former businesswomen and healthcare professional, she is UKIP's deputy chair and home affairs and justice spokeswoman.
She is regarded as the favourite but was criticised for not taking part in any of the election hustings.
Elizabeth Jones is deputy chair of the party's Lambeth branch. She stood unsuccessfully in May's London Assembly elections and came fifth in July's Tooting by-election.
She is a family law solicitor and a member of the party's national executive committee.
She has said she will bring a fresh approach and different style of leadership, urging a focus on trade and education in the wake of the vote to leave the EU.
Who did not stand
- Steven Woolfe was barred from standing as he missed the deadline for submitting his nomination papers. He blamed "technical issues" for sending the paperwork online late. Mr Woolfe also admitted he failed to disclose a drink-driving ban from 2002 when seeking election as a police and crime commissioner a decade later.
- Suzanne Evans, a Conservative councillor who defected to UKIP in 2013. Currently suspended from the party until September following an internal dispute.
- Clacton MP Douglas Carswell, the party's best-known figure aside from Mr Farage. He ruled himself out of the contest, saying he would not endorse anyone.
- Deputy leader Paul Nuttall also ruled himself out, saying he had achieved his objective of getting the UK out of the EU.