A filament of 70% cellulose and 30% lignin having a titer of 1000 dtex in conditioned state and consisting of 400 single fibers with a diameter of 15 µm was prepared using the Ioncell® process. In a preliminary screening, the stabilization conditions were optimized. Subsequently, the filament was continuously stabilized using impregnation with diammonium sulfate solutions and thermal treatment at 250 °C. The stabilized filament was then carbonized in two additional thermal processing steps, first in 40 min up to 900 °C, followed by heat temperature carbonization at 1500 °C for 2 min. In comparison to carbon fibers from a pure cellulose precursor, the yield could be significantly increased. Through variation of fiber tension, a first optimization of the mechanical properties of the prepared carbon fibers could be achieved. Extensive carbon characterization revealed the changes in molecular structure during the applied thermal treatments. The achieved mechanical properties of tensile strength >1 GPa and tensile modulus >100 GPa at yields >35% are very promising and show great potential as a sustainable carbon fiber alternative upon further optimization.