Breeding season for P. regilla extends from January to mid-May. During this time, females lay eggs which are brown and yellow. Males externally fertilize the eggs, which are usually laid in gently moving water, in clutches of 5 to 70 eggs, and must be kept moist.
Pacific treefrog tadpoles are of medium size, typically about 46.6 mm long, and brown in color. Tadpole tails are not flagellated. Pacific tree frogs show rapid growth during the first summer after hatching. Tadpoles undergo metamorphosis between 50 and 80 days of age. During the metamorphosis, individuals typically measure between 12 and 15 mm long. Within two months of metamorphosis, individuals approximately double in length. Newly metamorphosed frogs leave the breeding area and seek habitats similar to that of an adult frog. Pacific treefrogs reach sexual maturity quickly and participate in the first mating chorus following their hatching.