Rebecca Long Bailey has said she privately argued against Labour supporting a second Brexit referendum.
The shadow business secretary has formally announced her bid to succeed Jeremy Corbyn as party leader.
Long Bailey, the likely main challenger to shadow Brexit secretary Keir Starmer, is seen as the favourite of the current leadership.
Starmer was instrumental in shifting Labour’s position towards a promising a public vote on any Brexit deal.
Speaking to BBC Radio 4′s Today programme on Tuesday morning, Long Bailey said Labour had not been “trusted on Brexit” at the election.
“When I knocked on a Remain voter’s door they thought we were a Leave party. When I knocked on a Leave voter’s door they thought we were a Remain party,” she said.
“We were losing trust with our communities who voted Leave because they were very clear they wanted the Brexit issue resolved as quickly as possible.”
She added: “Everything we were trying to say in the media was confusing to voters.”
Asked if she argued against Labour moving to a position of supporting another public vote, Long Bailey said: “I certainly did.
“I was very focused on making the point we were trying to get a good deal, I think that should have been a very strong message on everything that we said.”
Her comments appear at odds with what she told the BBC’s Andrew Marr Show in October when she had “been on a journey” and supported a public vote.
Long Bailey said today that while Corbyn had to accept “ultimate responsibility” for Labour’s heavy election defeat, she still backed him.
“I still support Jeremy because I felt that he was the right man with the right moral integrity to lead the party,” she said.
Long-Bailey’s announcement came as the party’s ruling National Executive Committee (NEC) set out the timetable for election, with the new leader to be announced at a conference on April 4.
In addition to Long-Bailey and Starmer, four other candidates have announced they intend to stand for the leadership – frontbenchers Emily Thornberry and Clive Lewis, and backbenchers Jess Phillips and Lisa Nandy.