The slender mongoose lives alone or in pairs. They remain in the same area and dens may be found anywhere sheltered from the elements: in crevices between rocks, in hollow logs, and the like.
Slender mongooses are polygynandrous (promiscuous), both males and females have multiple mates. Breeding is seasonal and occurs during the short rain season in October-November or long rain season in February-April. Females usually produce 1-2 litters per breeding season consisting of 2-4 pups. The gestation period lasts around 57-65 days. Pups are born blind and weigh around 20 g. Their eyes open when they are 3 weeks old. They begin to eat solid food at about 28 days and are weaned at 55-71 days.
Young become independent from their mothers when they are 6 months old. Males become reproductively mature at 10-12 months of age, while females reach maturity when they are 2 years old.