Alina Habba, 40, defended Trump earlier this year, also serving as his legal spokeswoman.
Habba has been spending time with the US president-elect since the election at his Florida club Mar-a-Lago.
"She has been unwavering in her loyalty and unmatched in her resolve — standing with me through numerous 'trials,' battles and countless days in Court," Trump posted on his social network Truth Social.
"Few understand the Weaponization of the 'Injustice' System better than Alina."
Alina Habba has been spending time with Trump since the election at his Florida club Mar-a-Lago. (AP PHOTO)
Trump became the first former American president to be convicted of felony crimes when a New York jury in May found him guilty of all 34 charges in a scheme to illegally influence the 2016 election through a hush money payment to a porn actor who said the two had sex.
In Trump's first term, the position of counsellor was held by Republican strategist Kellyanne Conway.
Habba has Iraqi ancestry and is Chaldean, which is Iraq's largest Christian denomination and one of the Catholic Church's Eastern rites.
Habba frequently accompanied Trump on the campaign trail and was one of the speakers at the late October rally in New York's Madison Square Garden.
On Sunday, Trump also announced he is bringing back former staffer Michael Anton to serve as director of policy planning at the State Department. Anton served as the National Security Council spokesman from 2017 to 2018.
Trump said he also will be appointing Michael Needham, a former chief of staff for Senator Marco Rubio, as counsellor of the State Department. The Florida senator was chosen by Trump to be his next secretary of state.
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