The South Antrim Assembly member was appointed leader in Novermber 2019.
He has written to the UUP chairman asking him to accept his resignation from Monday.
The announcement comes amid growing internal UUP concern at his leadership.
In the letter, Mr Aiken said the past few months have been a momentous time for our Union and for Northern Ireland and that he believes Unionism needs positive, hopeful and progressive leadership.
He adds: To represent the brand of Unionism that builds on hope and not fear, and provides a clear, modern, alternative, that will be both the future of our Party and Northern Ireland will require strong leadership.
Mr Wright passed away suddenly in Portadown on Saturday morning at the age of 48.
With the historic family farm based in Armagh for five generations, the news of the highly respected man s passing has left the local community in shock, alongside tributes from the wider food industry on the significant mark he made.
Paying tribute to the former rugby player, who represented Ulster at under-age level, Portadown Rugby Club said that they were greatly saddened to hear of his death. Dean was a barnstorming open side flanker who came through the youth system at the club, they added. Unfortunately, Dean s shoulders couldn t withstand the ferocity of his tackling and he was forced to retire from the game early when a promising career beckoned.
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