Teams had already spent a combined £1.005bn as of 08:30 BST on Wednesday, shattering last year's record £870m.
Thirteen top-flight teams broke their own transfer records.
The 20 clubs in the Premier League have benefited from a record £5.1bn television deal which came into effect this season.
"As has been the case for a number of years now, the increases in broadcast revenue, with the 2016-17 season being the first of the new broadcast deal cycle, is the principal driver of this spending power," said Dan Jones, a partner at financial analyst Deloitte.
While this year's figure of £1.165bn easily broke the record set 12 months ago, it dwarfed the £215m spent during the first window in the 2003-04 campaign.
Such financial strength owes much to the record £5.136bn domestic TV deal, which was more than £2bn larger than the previous contract from 2013 to 2016.
Ex-England winger Trevor Sinclair said: "There's so much money in it for a reason - supply and demand.
"People demand to see the Premier League. If anyone is going to get the financial gain, surely it has to be the players, they are the ones who make it happen."
Such financial strength owes much to the record £5.136bn domestic TV deal, which was more than £2bn larger than the previous contract from 2013 to 2016.
Ex-England winger Trevor Sinclair said: "There's so much money in it for a reason - supply and demand.
"People demand to see the Premier League. If anyone is going to get the financial gain, surely it has to be the players, they are the ones who make it happen."
