Author Damian Barr, who led a campaign to have the vice-president of the Booker Prize removed for "homophobic views" has been accused of transphobia.
Organisers cut ties with Lady Nicholson of Winterbourne, whose late husband helped to found the Booker, last week.
Barr had accused her of "very public and very powerful homophobia" because of her opposition to gay marriage.
He has now apologised for using derogatory terms to refer to transsexuals on social media.
In one post, the author also appeared to mock a transsexual who had attempted to take their own life.
'Unkind and hurtful'
Mr Barr says he has now changed his language to reflect his belief that trans people "deserve dignity".
The author's statement came via his literary agency - which publicly backed his action against Lady Nicholson by praising his "fearless determination to call out all forms of prejudice".
In it he apologised for what he calls a "handful of tweets which have been dug up and circulated to hurt trans people and divide the gay and transgender community.
"I have long said that words equal power," he sad. "In the past, I have used the word 'tr-nny'. Flippantly not maliciously. But it is an unkind and hurtful word I'm embarrassed to have used.
"I apologised then. I remain sorry today. I listened and changed: I hope my solidarity and actions since speak louder than that word then."
The author, who rose to fame with his memoir of growing up gay in Margaret Thatcher's Britain, Maggie and Me, has subsequently locked his Twitter account.
The Savoy, for which Mr Barr is the literary ambassador, issued a statement saying it is a supporter of all LGBT+ communities and condemned any form of discrimination.
It said: "We wish to make it very clear that we do not condone Mr Barr's comments and that we welcome his recent apology. The Savoy is an ally to all communities - as colleagues, guests and visitors."
The Booker Foundation removed Lady Nicholson from her honorary position as vice-president last week, after an outcry from some in the literary world about her alleged homophobic and transphobic views.
The campaign began when Munroe Bergdorf, the model and transgender activist, said she was referring Lady Nicholson to the Parliamentary Standards Conduct Commissioner over posts on social media about the trans community.
Mr Barr subsequently called for her removal, and was later joined by Booker prize-winner Marlon James and the bestselling novelist Sarah Perry, amongst others.
Lady Nicholson voted against gay marriage in 2013, but has consistently denied charges of homophobia.
"I did indeed vote against same-sex marriage in 2013," she told the Guardian. "I have not yet learned from my critics how I am offending by perceived homophobia. In other words, they have offered no evidence."