"Defender Eliaqium Mangala has joined Everton on loan until the end of the season, subject to Premier League clearance," a statement read on City's official website.
The France international has failed to impress since Pep Guardiola took charge at the Etihad. Mangala's deadline day transfer to the Merseyside club will be his second loan spell as he spent the 2016/17 season with Valencia.
The City manager has deployed John Stones and Nicolas Otamendi as his first choice centre-backs when captain Vincent Kompany was not available for selection this term. The former two have been the key figures in their side's defence that has seen them concede only 18 goals in 25 games.
Mangala saw his first-team appearances being limited as he has started only in four Premier League games this term. He was behind Kompany, Stones and Otamendi in the pecking order.
Guardiola's side added Aymeric Laporte to their squad as the Frenchman arrived at the Etihad from Athletic Bilbao for a club record fee of £57m. Laporte's arrival saw Mangala drop further down the pecking order and thus a loan move was the best option for the player.
A temporary switch to Everton will help the central defender get regular playing time until the end of this campaign. It will also boost the former FC Porto star's chances of making it to the France squad for the 2018 World Cup in Russia. Mangala said he is "thrilled to have the opportunity" to play for the Toffees.
"I am thrilled to have the opportunity to play for Everton and I cannot wait to pull on the royal blue jersey for the first time and give my all for the supporters," Mangala told Everton's official website.
Allardyce has the services of club captain Phil Jagielka, Ashley Williams and last summer signing Michael Keane as the first choice centre-backs at Everton. The arrival of Mangala will further strengthen their heart of the back four for the second-half of the season.