The current study aimed at characterizing the dynamics of SARS‐CoV‐2 nucleocapsid (N) antigenemia in a cohort of critically ill adult COVID‐19 patients and assessing its potential association with plasma levels of biomarkers of clinical severity and mortality. Seventy‐three consecutive critically ill COVID‐19 patients (median age, 65 years) were recruited. Serial plasma (n = 340) specimens were collected. A lateral flow immunochromatography assay and reverse‐transcription polymerase chain reaction (RT‐PCR) were used for SARS‐CoV‐2 N protein detection and RNA quantitation and in plasma, respectively. Serum levels of inflammatory and tissue‐damage biomarkers in paired specimens were measured. SARS‐CoV‐RNA N‐antigenemia and viral RNAemia were documented in 40.1% and 35.6% of patients, respectively at a median of 9 days since symptoms onset. The level of agreement between the qualitative results returned by the N‐antigenemia assay and plasma RT‐PCR was moderate (k = 0.57; p < 0.0001). A trend towards higher SARS‐CoV‐2 RNA loads was seen in plasma specimens testing positive for N‐antigenemia assay than in those yielding negative results (p = 0.083). SARS‐CoV‐2 RNA load in tracheal aspirates was significantly higher (p < 0.001) in the presence of concomitant N‐antigenemia than in its absence. Significantly higher serum levels of ferritin, lactose dehydrogenase, C‐reactive protein, and D‐dimer were quantified in paired plasma SARS‐CoV‐2 N‐positive specimens than in those testing negative. Occurrence of SARS‐CoV‐2 N‐antigenemia was not associated with increased mortality in univariate logistic regression analysis (odds ratio, 1.29; 95% confidence interval, 0.49‐3.34; p = 0.59). In conclusion, SARS‐CoV‐2 N‐antigenemia detection is relatively common in ICU patients and appears to associate with increased serum levels of inflammation and tissue‐damage markers. Whether this virological parameter may behave as a biomarker of poor clinical outcome awaits further investigations. Highlights SARS‐CoV‐2 N‐antigenemia occurs frequently in ICU patients. SARS‐CoV‐2 N‐antigenemia occurs more frequently in ICU patients with viral RNAemia. SARS‐CoV‐2 N‐antigenemia associates with high serum levels of inflammatory biomarkers.