This data was collected and analysed for the project "Dissolved inorganic nitrogen uptake by seaweeds: a global analysis" published in Botanica Marina. Data was compiled between May 2025 and July 2025 from published studies on the uptake kinetics of nitrate (NO₃⁻) and ammonium (NH₄⁺) by marine macroalgae i.e. the rate of Dissolved Inorganic Nitrogen (DIN) uptake rate at a range of DIN concentrations. Each study contained values for the Michaelis-Menten kinetic constants maximum uptake rate (Vmax) and the half saturation constant (Ks), linear uptake gradients, or described biphasic uptake patterns. A total of 84 published studies presenting this data were discovered, with 556 distinct data entries. The project examined DIN uptake rates in marine macroalgae by Phylum, order, experimental irradiance and temperature, geographic location and functional group. Articles were identified through searches on Google Scholar and Web of Science, with all studies reporting Michaelis-Menten kinetic constants or linear uptake slopes included. For each study, we recorded taxonomic information, functional group, the experimental subject (species and algal tissue used), habitat of origin (subtidal, intertidal, or cultured), and season of collection. We also documented experimental conditions, including temperature, irradiance, DIN source (nitrate or ammonium), presence and concentration of other macronutrients (e.g., phosphate or non-target DIN), and the phosphate:DIN ratio of the culture medium. Where available, we extracted kinetic parameters (Vmax, Ks/Km), linear uptake slopes, uptake pattern (saturating, linear, or biphasic), maximum DIN concentration tested, the range of concentrations used in multi-flask experiments, and the time interval over which uptake was measured (for time-course experiments). Geographic coordinates of the study location were also recorded. Each study entry in this dataset includes the full study reference (author and year) and a functional DOI where available (as of November 2025).