long-serving
adjective[before noun]
HR,WORKPLACEukushavingworkedfor the sameorganization, or having had the samejobfor alongtime:
long-serving employees/staffThe Railroad RetirementActallowedlong-servingemployeestoretirewithfullbenefitstwoyearsearlier.
along-servingboss/chiefexecutive/manager