Background The Nine-Hole Peg Test (9HPT) is the golden standard in clinical practice to measure manual dexterity in people with multiple sclerosis (MS). However, administration requires trained personnel and dedicated time during a clinical visit. Objective To validate a smartphone-based test for remote manual dexterity assessment, the icompanion Finger Dexterity Test (FDT), to be included into the icompanion application. Methods 65 MS and 81 healthy subjects performed a first testing session, and 21 healthy subjects performed a second session approximately two weeks later. Results The FDT significantly correlated with the 9HPT (dominant: Spearman{\textquoteright}s ρ=0.62, p<0.001; non-dominant: ρ=0.52, p<0.001). FDT scores showed a significant difference between the MS and healthy subjects (dominant: Cohen{\textquoteright}s d=0.24, p=0.015; non-dominant: Cohen{\textquoteright}s d=0.18, p=0.013), which was not the case for the 9HPT. A significant correlation with age (dominant: ρ=0.46, p<.001; non-dominant: ρ=0.40, p=0.002), Expanded Disability Status Scale (EDSS, dominant: ρ=0.37, p=0.004; non-dominant: ρ=0.33, p=0.017), and disease duration for the non-dominant hand (ρ=0.31, p=0.016) was observed. Conclusion The icompanion Finger Dexterity Test shows a moderate-to-good concurrent validity, ecological validity and test-retest reliability, and differentiates between the MS subjects and healthy controls. This test can be implemented into routine MS care for remote follow-up of manual dexterity.