AimsGATA‐binding protein 3 (GATA3) is a well‐studied transcription factor found to be essential in the development of luminal breast epithelium and has been identified in a variety of tumour types, including breast and urothelial carcinomas, making it a useful immunohistochemistry marker in the diagnosis of both primary and metastatic disease.Methods and resultsWe investigated GATA3 protein expression in a 106 primary triple‐negative breast carcinomas (100 basal‐like, six non‐basal‐like) using Cell Marque mouse monoclonal anti‐GATA3 (L50‐823). Reverse transcription–quantitative polymerase chain reaction (RT–qPCR) was used to quantify mRNA expression in 22 triple‐negative breast cancers (TNBCs) (20 primary and two cell lines), four luminal (three primary and one cell line) and five human epidermal growth factor receptor 2 (HER2) (four primary and one cell line) amplified tumours. In 98 TNBCs where IHC was assessable, 47 (48%) had a 1+ or greater staining with 20 (21%) having high GATA3 expression when using a weighted scoring.ConclusionOur study has demonstrated that GATA3 expression is common in primary triple‐negative breast carcinomas. It also suggests that although GATA3 is an oestrogen receptor (ER) regulated gene, it still proves useful in differentiating between primary and metastatic tumours in patients with a history of breast cancer regardless of its molecular subtype.