Coccidiosis caused by Eimeria tenella is a parasitic disease affecting chickens. In Pakistan, there has been no previously published report on phylogenetic analysis of Eimeria tenella. In this retrospective study, tissue samples were collected from a flock of clinically infected chicken followed by haematology, serum biochemistry, and histopathology. Species specific PCR based on polymorphic site of the ITS1 gene was developed and used to identify the organism. Haematological examination of the blood demonstrated a decrease in total erythrocytes, packed cell volume, haemoglobin concentration, and red blood cell indices. Differential leukocyte analysis revealed leukocytosis, heterophilia, eosinophilia, monocytosis, and lymphocytosis. Serum biochemistry showed marked elevation in aspartate transaminase, alkaline phosphatase and creatinine and a significant decline in alanine transaminase, total protein, total albumin, globulin, triglycerides and cholesterol values. Histopathological examination demonstrated degenerative changes, necrosis haemorrhages, and sloughing off epithelial cells of broad folds of caeca, mild lymphoplasmacytic infiltration in the periportal area of the liver and mild depletion of lymphocyte in the bursa of Fabricius. The seven clades of avian Eimeria species strongly support that E. necatrix and E. tenella were closely associated and placed in the same sister clade with high bootstrap support (98%). Our two isolates RSI and RSII showed a homology index of 99.82% (nucleotide level) and 99.47% (amino acid level) with each other. The maximum similarity percentage indicated that RSI and RSII isolates were closely related to strains reported from India and China. This study is the first report on molecular characterization of E. tenella in Pakistan highlighting the pathological potential and distribution of E. tenella.