London — Tullow Oil’s CEO Paul McDade and exploration director Angus McCoss quit after the company cut its production outlook and suspended the dividend, sending shares tumbling more than 60%.

McDade and McCoss resigned with immediate effect, marking the exit of Tullow’s old guard after founder Aidan Heavey departed in 2018. Both had been stalwarts at the company for over a decade, presiding over discoveries from West Africa to Guyana, but also a slew of recent operational setbacks...