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The diet of Pteraster tesselatus includes encrusting sponges, bryozoans, hydroids and colonial sea squirts, and less frequently, sea anemones, the rock oyster Pododesmus macrochisma, scallops and solitary sea squirts.

P. tesselatus breeds from early July to the end of August. It does not brood its eggs in the so-called nidamental chamber. Instead, it releases yellow or orange eggs (1.5 mm in diameter) through the osculum two or three at a time or in a long string. The fertilized egg develops into a nonfeeding larva that passes directly into the adult without metamorphosis, which usually results in the axes of symmetry changing or the loss of larval structures. This is the only sea star known to have truly direct development. McEdward (1995) suspects that the larval form evolved in a brooding ancestor but did not revert back to a typical pelagic larva when the species evolved back to broadcast spawning. At 10°C in the laboratory, development from egg to young sea star took 25 days; the mouth formed on the 30th day. This implies that, in nature, this sea star does not feed until it settles on the substrate as a juvenile. Most settlement occurs between 10 and 12 days, often among the tubes of the polychaete Phyllochaetopterus. See McEdward 1992 for details of the unusual development of this species.

P. tesselatus shows a negative response to bright light and a positive response to moderate or green light. When it is disturbed, cells in its supradorsal membrane secrete copious amounts of mucus, which is forced out of the spiracles onto the top surface by water pressure in the nidamental chamber. This secretion is highly effective in repelling predation by Solaster dawsoni and Pycnopodia helianthoides; experimental removal of the supradorsal membrane allowed an S. dawsoni to eat a P. tesselatus in four days. If a clam is injected with P. tesselatus mucus and offered to the Sunflower Star, it is rejected. In an aquarium, this mucus will kill snails, hermit crabs and sea cucumbers that are submersed in it for 24 hours.

P. tesselatus flushes its gills by inflating its supradorsal membrane to draw in sea water through slits between the adambulacral spines, and contracting the membrane to force water out through the osculum. This allows the animal to regulate its oxygen intake. The scale worm Arctonoe vittata is commensal on P. tesselatus.