A good dispersion of single-walled carbon nanotubes (SWCNTs) in liquid media is a prerequisite to fulfill many of their applications. This contribution reports an efficient approach to additive-free dispersion of SWCNTs with the aid of functionalized carbonaceous byproducts (CBs, e.g., amorphous carbon, carbon nanoparticles, and carbonaceous fragments) in SWCNT products. SWCNT bundles are treated by oleum intercalation and nitric acid oxidation in sequence, which leads to the selective functionalization of the CBs while the structure and properties of the SWCNTs are well preserved. These functionalized CBs can improve the subsequent dispersion of SWCNTs and the majority of SWCNTs in the suspension are present in small bundles or individually. Moreover, SWCNT transparent conductive films (TCFs) are fabricated by using these suspensions. The SWCNT TCFs obtained can achieve a low sheet resistance of 76 and 133 Ω sq−1, with optical transmittance of 82% and 90% at 550 nm, respectively.