CMC is used in food science as a viscosity modifier or thickener, and to stabilize emulsions in various products including ice cream. As a food additive, it has E number E466. It is also a constituent of many non-food products, such as K-Y Jelly, toothpaste, laxatives, diet pills, water-based paints, detergents, textile sizing and various paper products. It is used primarily because it has high viscosity, is non-toxic, and is hypoallergenic. In laundry detergents it is used as a soil suspension polymer designed to deposit onto cotton and other cellulosic fabrics creating a negatively charged barrier to soils in the wash solution. CMC is used as a lubricant in non-volatile eye drops (artificial tears). Sometimes it is methyl cellulose (MC) which is used, but its non-polar methyl groups (-CH₃) do not add any solubility or chemical reactivity to the base cellulose.

Following the initial reaction the resultant mixture produces approximately 60% CMC plus 40% salts (sodium chloride and sodium glycolate). This product is the so-called Technical CMC which is used in detergents. A further purification process is used to remove these salts to produce pure CMC which is used for food, pharmaceutical and dentifrice (toothpaste) applications. An intermediate "semi-purified" grade is also produced, typically used in paper applications.

CMC is also used in pharmaceuticals as a thickening agent. CMC is also used in the oil drilling industry as an ingredient of drilling mud, where it acts as a viscosity modifier and water retention agent. Poly-anionic cellulose or PAC is derived from cellulose and is also used in oilfield practice. CarboxyMethyl Cellulose (CMC) is both chemically and physically distinguished from Polyanionic Cellulose. CMC is definitely a Carboxylic Acid, where PAC is Ether. Although CMC and PAC are manufactured from the same raw materials, by adjusting the type of cellulose and stoichiometry of the reactants different final products may be produced. The primary difference between the CMC and PAC production processes is in the radicalization step.^{[citation needed]}

Insoluble microgranular carboxymethyl cellulose is used as a cation-exchange resin in ion-exchange chromatography for purification of proteins.^[2] Presumably the level of derivatization is much lower so that the solubility properties of microgranular cellulose are retained while adding sufficient negative charged carboxylate groups to bind positively charged proteins.

CMC is also used in ice packs to form a eutectic mixture resulting in a lower freezing point and therefore more cooling capacity than ice.^[3]

Aqueous solutions CMC have also been used to disperse carbon nanotubes. It is thought that the long CMC molecules wrap around the nanotubes, allowing them to be dispersed in water. In conservation-restoration it is used as an adhesive or fixative (commercial name Klucel).