Joe Atkinson today changed his plea to admit the killing of Poppy, 24.
The murder took place at the Saxton flats development in the Richmond Hill area of the city on December 14 last year. The pair are believed to have been in a relationship and to have lived together in the apartment.
Atkinson, 25, had pleaded not guilty to the murder charge when he appeared before Leeds Crown Court on January 17 this year.
The case was returned to the court this morning where Atkinson's barrister, Richard Wright, QC, asked for the murder charge to be put to him again by the court clerk.
Atkinson spoke only to confirm his name and enter the guilty plea.
The public gallery was full with Miss Devey Waterhouse's relatives and police officers involved in the case.
Atkinson's parents were also present for the brief hearing.
Prosecutor Jason Pitter, QC, asked for the case to be adjourned until next Friday (April 12) when Atkinson will be sentenced.
Mr Justice Lavender adjourned the case until that date and told Atkinson he will have to remain in custody until then.
Emergency services were called to the apartment block in the Richmond Hill area just before 9am.
A post-mortem examination found Miss Devey Waterhouse's preliminary cause of death as head and neck trauma.
Poppy was a University of Nottingham maths graduate who is originally from Somerset.
She had a Masters degree in statistics and began a job as a quantitative trading analyst at bookmaker William Hill's Leeds offices in 2017.
A spokesman for the company said at the time of of the incident: "I can confirm she was an employee and that we are providing support to her colleagues, who are clearly very shocked and saddened."
Atkinson is a former Wetherby High School pupil who also studied at the University of Nottingham.
Photos on Poppy's Instagram account show that the pair had travelled extensively together in the past few years, visiting destinations such as Bolivia, the Grand Canyon, Iceland, Sweden and San Francisco, and enjoying a visit to the Wimbledon tennis championships.