<p>Ethiopian durum wheat (<i>Triticum turgidum</i> ssp. <i>durum</i> Desf.) landraces represent an important reservoir of genetic diversity for wheat improvement, climate adaptation, and conservation. This study evaluated the phenotypic diversity and population structure of 520 durum wheat genotypes, comprising 484 Ethiopian landraces and 36 improved cultivars, using nine qualitative and four phenological traits. Field experiments were conducted during the 2024 main cropping season at two locations in Ethiopia. Phenotypic diversity was assessed using the Shannon–Weaver diversity index, analysis of variance, factor analysis of mixed data (FAMD), and unweighted pair group method with arithmetic mean (UPGMA) clustering. Highly significant variation (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(P&lt;0.001\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mo>&lt;</mo> <mn>0.001</mn> </mrow> </math></EquationSource> </InlineEquation>) was detected among geographic origins and altitudinal classes for most evaluated traits. Mean within-population diversity (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({H}_{s}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <mi>s</mi> </msub> </math></EquationSource> </InlineEquation>) was higher across altitude classes (0.74) than across geographic groupings (0.48), whereas total diversity remained high (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({H}_{t}=0.78\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>H</mi> <mi>t</mi> </msub> <mo>=</mo> <mn>0.78</mn> </mrow> </math></EquationSource> </InlineEquation>). Population differentiation was substantially greater among geographic origins (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({G}_{st}=0.228\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>G</mi> <mrow> <mi mathvariant="italic">st</mi> </mrow> </msub> <mo>=</mo> <mn>0.228</mn> </mrow> </math></EquationSource> </InlineEquation>) than among altitude classes (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({G}_{st}=-0.051\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>G</mi> <mrow> <mi mathvariant="italic">st</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <mn>0.051</mn> </mrow> </math></EquationSource> </InlineEquation>), indicating that geographic origin played a stronger role than altitude in structuring phenotypic diversity. Multivariate analyses showed that phenological traits, particularly days to heading, days to booting, days to maturity, and grain filling period, contributed most strongly to population differentiation and adaptive variation. FAMD further revealed a complex multidimensional phenotypic structure, with the first five dimensions explaining 37.8% of the total variation. Cluster analysis grouped approximately 84% of the genotypes into four major clusters, while the remaining genotypes formed several distinct peripheral groups, particularly from geographically isolated regions such as Bench Maji and Jimma. The results demonstrate that Ethiopian durum wheat landraces maintain extensive phenotypic diversity structured primarily by geographic origin rather than altitudinal distribution. The substantial variation identified in phenological, spike, and seed-related traits highlights the importance of Ethiopian landraces as valuable genetic resources for conservation and breeding programs aimed at improving climate resilience, adaptation, and grain quality in durum wheat.</p>