The 68-year-old had been a prominent backer of Mr Trump during the 2016 election campaign.
But she has now criticised the president after a leaked government memo emerged, containing proposals that would fundamentally alter how gender is defined in the US.
An unreleased report from the Department for Health and Human Services called for a tightening of the legal definition of sex, under which transgender and non-binary individuals would be completely excluded.
Under the proposed policy, gender would be determined by a “biological basis that is clear, grounded in science, objective, and administrable”.
If enforced, the suggested definition would revoke civil rights protections for transgender people and would reverse a series of policies instituted by the administration of Barack Obama, which essentially allowed gender to be the choice of individuals.
In a separate controversy, US diplomats are said to be lobbying to replace the word “gender” with “woman” in UN human rights documents, in what has also been interpreted as a move to marginalise the transgender community.
Now, in an op-ed titled I Was Wrong, published in the Washington Post, Jenner has joined those criticising the Trump administration.
“Trump was the first Republican presidential candidate to claim to support this valuable, vulnerable community,” Jenner wrote ”and I was encouraged by the applause he received when he said at the Republican National Convention in July 2016 that he would stand up for the LGBTQ community.”
“Sadly, I was wrong.”
Jenner, who was born Bruce and was an Olympic gold medal-winning decathlete, revealed her identity as a trans woman in April 2015.
She accused Mr Trump of treating the trans community as “political pawns” .
Jenner wrote: “The reality is that the trans community is being relentlessly attacked by this president.”
“The leader of our nation has shown no regard for an already marginalized and struggling community. He has ignored our humanity. He has insulted our dignity.”
“This is politics at its worst. It is unacceptable, it is upsetting, and it has deeply, personally hurt me.”
Additional reporting by agencies
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies