Dark matter search results from the complete exposure of the PICO-60 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> bubble chamber

Final results are reported from operation of the PICO-60 ${\mathrm{C}}_{3}{\mathrm{F}}_{8}$ dark matter detector, a bubble chamber filled with 52 kg of ${\mathrm{C}}_{3}{\mathrm{F}}_{8}$ located in the SNOLAB underground laboratory. The chamber was operated at thermodynamic thresholds as low as 1.2 keV without loss of stability. A new blind 1404-kg-day exposure at 2.45 keV threshold was acquired with approximately the same expected total background rate as the previous 1167-kg-day exposure at 3.3 keV. This increased exposure is enabled in part by a new optical tracking analysis to better identify events near detector walls, permitting a larger fiducial volume. These results set the most stringent direct-detection constraint to date on the weakly interacting massive particle (WIMP)-proton spin-dependent cross section at $3.2\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}41}\text{ }{\mathrm{cm}}^{2}$ for a 25 GeV WIMP, improving on previous PICO results for 3--5 GeV WIMPs by an order of magnitude.