Optimism bias and positive attention bias are both important for mental health. They have only been examined separately, even though the combined cognitive biases hypothesis suggests that cognitive biases interact and mutually enforce each other. Examining interactions between optimism and positive attention bias can reveal how the biases are maintained over time and thereby contribute to mental health. Thus, the current studies’ goals were to investigate the relation between optimism and attention bias and its underlying somatovisceral and neural mechanisms. Studies 1 and 2 showed that optimistic expectancies causally influence attention. Induced optimistic (and pessimistic) expectancies led to enhanced attention orientation and maintenance on rewarding (and punishing) information. This was reflected in shortened reaction times and eye gaze on expected information as well as larger pupil size and enhanced salience and executive control network activity (e.g., insula and anterior cingulate cortex) for unexpected information following both optimistic and pessimistic expectancies. Notably, optimistic expectancies had a stronger influence on attention deployment than pessimistic ones – accompanied by enhanced insula activation during reorientation of attention to punishing information following optimistic expectancies. Study 3 revealed that positively biased attention also causally influences optimism bias. Performing a two-week attention bias modification training guiding attention toward accepting and away from rejecting face stimuli enhanced optimism bias whereas performing a neutral control attention training did not. Our findings provide first empirical support for mutual optimism-attention-bias interactions and therefore explain how the two biases are maintained, possibly leading to an upward spiral of positivity that protects mental health.