The note also said her husband, Ishaan - a 27-year-old telemarketer - would end his life by jumping off a building in Sector 25.
But it turned out during the investigation that the note had been written by the accused.
The body of the woman, a student in Noida, was found by housekeeping staff.
"We got a call around 6.30pm from the hotel that a body had been found. The woman was rushed to hospital but declared dead," SSP Praveen Kumar said.
Police first detained Ishaan's brother at his home town Mughalsarai in UP, following which the accused turned himself in at the Sector 18 police post at 9pm.
He confessed to killing his wife with a pillow and claimed he had also planned to commit suicide.
"They were married in June 2011. The accused said he had regular squabbles with his wife and that they were living separately," Kumar added.