We present millennial to centennial-scale monsoon variability during the Late-Pleistocene to Holocene using multi-proxy data from 100 cm thick peat deposit in the Baspa Valley, northwest Himalaya. Based on high-resolution mineral magnetism, carbon isotope, and total organic carbon data supported by radiocarbon dating, four climatic phases of alternating strengthened and weakened Indian summer monsoon (ISM) are identified for the last 20 kyr in the higher central Himalaya. Periods of strengthened ISM are dated to ${\sim}$15 to ${\sim}$14 ka, ${\sim}$10 to ${\sim}$7 ka, ${\sim}$2.4 to ${\sim}$1.3 ka, and 243 yr BP to present, which is ascribed to the post-Older Dryas associated with an increase in solar insolation. The phases of weakened ISM are bracketed between ${\sim}$20 and ${\sim}$15 ka, ${\sim}$14 to ${\sim}$10 ka, ${\sim}$7 to ${\sim}$2.4 ka, and ${\sim}$1300 to ${\sim}$243 yr BP. These phases are attributed to global cooling events, i.e., the Last Glacial Maximum (LGM), Younger Dryas (YD), and the Middle to Late Holocene. They govern by changes in the solar insolation.