"I will be retiring... With my head held high," the 39-year-old said at a press conference here.
"I think this is the right time as every sportsman has to take this decision in his career," he added, bringing an end to a 17-year Test career.
Younis, who has led Pakistan in all three formats and guided them to their only World Twenty20 title in England in 2009, needs only 23 runs to reach 10,000 Test runs.
Younis has so far scored 34 Test centuries in 115 matches -- the most by any batsman from the country -- and is set to become the first Pakistani and 13th batsman in the world to score 10,000 or more runs.
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He has so far accumulated 9977 runs at an average of 53.06. India's Sachin Tendulkar currently tops the charts with 15,921 runs in 200 matches.
"People are calling me and asking me not to make any announcement to leave but now is the time," Younis said.
"No player always remains fit, the motivation never remains the same, so this is the time when Younis should leave the field after the upcoming series in West Indies."
His best Test score - 313 against Sri Lanka in 2009 - is the third highest for Pakistan, after Hanif Mohammad's 337 and Inzamam-ul-Haq's 329.
He was recently named one of Wisden's Five Cricketers of the Year, following his contribution in Pakistan's 2-2 drawn series in England last summer.
"I was planning this for few months," he said of his decision to quit, adding, "I always tried to play for my team and for my country."
The West Indies series starts in Jamaica from April 21 followed by Tests in Barbados and Dominica.