Display omitted •Textile dyeing sludge pyrolysis showed higher char yield and lower condensate yield.•Alkali and alkaline earth metals promoted sludge pyrolysis and CaO can retain sulfur.•Catalytic pyrolysis led to lower iodine and higher MB adsorption values for chars.•Higher MB adsorption values were obtained by municipal sewage sludge chars.•Heavy metals risk of MC were lower than TC, both MC and TC showed slight risks. A comparative research was performed to evaluate the products yields and chars properties for pyrolysis of textile dyeing sludge (TDS) and municipal sewage sludge (MSS). The high fixed carbon (19.36 wt%) and low volatile (23.66 wt%) contents of TDS resulted in higher char yields and lower condensate yields. TDS char (TC) had a higher sulfur (S) retention efficiency than MSS char (MC) and CaO exhibited a great S retention effect in MC. More alkali and alkaline earth metals (e.g. Na, K, Mg and Ca) in MSS contributed to enhanced catalytic pyrolysis. In comparison to non-catalytic pyrolysis, chars from catalytic pyrolysis had lower iodine number and higher methylene blue (MB) adsorption value. MB adsorption values of MC (212.28–414.20 mg/g) were much higher than those of TC (84.32–156.07 mg/g). In contrast, heavy metals risk degrees of MC (4.20–7.56) were lower than those of TC (7.55–12.87), and heavy metals in TC and MC showed slight risks to environment.