The news was announced via Cricket West Indies on Monday. The two players were not included in the 2015 World Cup and were kept out after that too, forcing Bravo to retire in 2017.
The decision comes after West Indies' finished ninth among the 10 participating teams at the ICC Cricket World Cup 2019 in England earlier this year.
CWI said it will be hiring a regional coach to fill the vacancy as it aims to give West Indies coaches opportunities.
Pollard said: "I'm truly honoured to be appointed captain of the West Indies and I would like to thank Cricket West Indies' board of directors for placing their faith and confidence in me".
A CWI statement said that the task force carried out a "four-month review" and "benchmarked cricket selection systems around the world and incorporated feedback and contributions from current and former players, coaches, administrators, franchise CEOs and almost 2,700 fans across the Caribbean". The CWI said the move was aimed at improving West Indies' position on the rankings table in limited-overs cricket.
However, he brings massive leadership experience in the shortest format, having led Barbados Tridents in the Caribbean Premier League for five years and then also taking over at St Lucia Stars last season.More news: USA to preserve economic expansion
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As far as Pollard's national appointment is concerned, it means that ODI skipper Jason Holder and T20I captain Carlos Brathwaite are set to face the axe. He said the board was following the "best possible pratices for best possible outcomes".
Holder, however, will remain in charge of the Test side.
"Jason Holder is a very important force and he is still going to be our red ball captain".
The release said the Selection Task Force recommended the immediate introduction of "red ball" and "white ball" captains to support a long-term strategy to focus on the different formats of global cricket.
Jason Holder will revert to the Test captaincy alone as Pollard takes over from him in 50-over cricket and from Carlos Brathwaite in T20.