The 29-year-old Brathwaite, who famously hit four consecutive sixes off England's Ben Stokes to seal the 2016 World Twenty20 title, is among the Windies players to decide that the trip to Karachi is too dangerous.
The series of three back-to-back matches starts on Sunday.
"We had a few players that opted not to tour Pakistan, due to their or their families' security concerns and Cricket West Indies (CWI) have fully accepted their position," said West Indies selector Courtney Browne.
Several other key players, including star batsman Chris Gayle, will miss the series to prepare for the lucrative Indian Premier League which starts on April 7.
All-rounder Jason Mohammed has been named as stand-in skipper in Brathwaite's absence, while experienced wicketkeeper-batsman Ramdin is set to play his first international since 2016.
The 33-year-old's last T20 for the West Indies was in the final victory over England in Kolkata two years ago.
"Denesh brings a lot of experience and an opportunity to restart his international career," added former Windies wicketkeeper Browne.
"While he will be the primary wicketkeeper in the squad, we also have available Chadwick Walton and Andre Fletcher as back up."
Fellow World Twenty20 winners Marlon Samuels and leg-spinner Samuel Badree have also been named in the 13-man squad.
Karachi successfully hosted the Pakistan Super League final last weekend, and the visit of the Windies represents the next step for the country in its bid to host regular international cricket for the first time since a terrorist attack on the Sri Lankan team bus in Lahore in 2009.
"This tour is a further major step for our friends at the Pakistan Cricket Board (PCB) to bring their cricket back home, and we are pleased that our players and support staff have recognised this and supported this venture," said CWI chief executive Jonny Grave.
"We have made it very clear to the players and support staff that had personal reservations about this Tour that we fully understand and accept their position."
West Indies squad: Jason Mohammed (captain), Samuel Badree, Rayad Emrit, Andre Fletcher, Andre McCarthy, Keemo Paul, Veerasammy Permaul, Rovman Powell, Denesh Ramdin (wicket-keeper), Marlon Samuels, Odean Smith, Chadwick Walton, Kesrick Williams
First Published: March 30, 2018, 11:15 AM IST