The 14-year-old had not been seen since getting into difficulty swimming off Barry Island last Sunday.
Since then, more than 40 specialist officers had been engaged in a search for the missing teenager that also involved a helicopter and coastguards.
Yesterday, Chief Inspector Marc Lamerton, of South Wales Police, confirmed that a body had been found in the sea near Fontygary – about three miles from where Hollie was last seen alive.
Last night, police confirmed it was the missing teenager.
Community leaders described the announcement as “awful”.
Mr Lamerton said: “We can confirm that a body recovered from the sea near Fontygary in the Vale of Glamorgan has been formally identified as that of 14-year-old Hollie McClymont. The body was discovered by a police search team this afternoon.
“Our thoughts are with Hollie’s family at this difficult time.”
St Thomas Aquinas Secondary School pupil Hollie had gone to South Wales with her mother, Sarah, for a holiday.
Police said the family chose Barry Island because they have relatives living in the area.
The teenager was last spotted getting into difficulty at around 2:45pm off the coast of Whitmore Bay, a popular destination for tourists.
However, officers said emergency crews were not alerted to the incident until an hour after she was last seen, something coastguards said they were “dumbfounded by”.
Once the alarm had been raised, local rescuers were deployed, relying on the skills and local knowledge of RNLI crews.
But by the end of the first full day of searching, coastguards said they had exhausted their efforts to find the teenager and formally handed the investigation over to police.
Prior to the discovery, Mr Lamerton had said officers were being “pragmatic” in their search efforts.
“We have 40 officers working on this, including specialist search teams trained to work underwater and the force’s helicopter,” he said.
“As you can imagine, her family are devastated – both those visiting from Glasgow and those living here in Barry.
“Hollie has visited the area before, but at this point there is nothing to suggest there is anyone else involved.”
News of the discovery of a body in the hunt for Hollie was described as a “nightmare scenario” by locals.
Steffan Wiliam, a Barry resident and Plaid Cymru councillor at the Vale of Glamorgan
Council, said: “This is awful, awful news, the nightmare scenario we have all been worrying about.
“Our thoughts go out to the family at this awful time. The pain and grief they must be feeling now is terrible.”
He said that from the location where the police said the body was found, it appeared that the teenager had gone outside the bay.
Currents outside the relative protection of Whitmore Bay will carry an object up or down the coastline and eventually out to sea, he added. “It seems that she will have been outside the bay and the currents will have just carried her away,” Mr Wiliam said.
“As soon as you are outside the bay, you will be carried off in one direction or another.
“Inside the bay, there is a circular current.
“But this is just awful news for the family, the worst news they can have.”
Scores of tributes have been paid via social network sites such as Facebook.
One person wrote: “This is so sad. The summer should have been a happy time for her and her family. RIP.”