Speculation that the couple, who only confirmed their relationship in June, are set to marry began after Deeley was seen sporting a diamond ring as they held a champagne celebration with friends at London's Goring Hotel on Sunday (July 29).
The former Fame Academy co-hosts were said to have "looked very happy and excited", according to Heat.
A source revealed: "There was lots of congratulations and passing around of a ring, which was a rather large diamond from what I could see."
Deeley went on to tweet a picture of a ring emblazoned with a 'C' the following day (July 30), along with the caption: "Love this ring."
A spokesperson for the couple has declined to comment on the story.
Deeley and Kielty were first romantically linked in February, and comedian and broadcaster Kielty was overheard confirming their relationship shortly afterwards.