| POS | Rank | Heat | BIB | ATHLETE | COUNTRY | RESULTS | ms* | 
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 667 | Steven GARDINER | 
 BAH                 | 
                43.89 Q NR | |
| 2 | 2 | 1 | 1071 | Nathon ALLEN | 
 JAM                 | 
                44.19 Q PB | |
| 3 | 1 | 2 | 1282 | Wayde VAN NIEKERK | 
 RSA                 | 
                44.22 Q | |
| 4 | 1 | 3 | 708 | Isaac MAKWALA | 
 BOT                 | 
                44.30 Q | |
| 5 | 2 | 2 | 712 | Baboloki THEBE | 
 BOT                 | 
                44.33 Q | |
| 6 | 3 | 1 | 1413 | Fred KERLEY | 
 USA                 | 
                44.51 q | |
| 7 | 2 | 3 | 1084 | Demish GAYE | 
 JAM                 | 
                44.55 Q PB | |
| 8 | 3 | 2 | 1266 | Abdalelah Haroun | 
 QAT                 | 
                44.64 q SB | |
| 9 | 4 | 2 | 961 | Matthew HUDSON-SMITH | 
 GBR                 | 
                44.74 SB | |
| 10 | 3 | 3 | 1431 | Gil Roberts | 
 USA                 | 
                44.84 | |
| 11 | 4 | 1 | 688 | Kévin BORLÉE | 
 BEL                 | 
                45.10 | |
| 12 | 5 | 1 | 1422 | Wilbert LONDON | 
 USA                 | 
                45.12 | |
| 13 | 4 | 3 | 766 | Jamal Walton | 
 CAY                 | 
                45.16 | .157 | 
| 14 | 6 | 1 | 871 | Óscar HUSILLOS | 
 ESP                 | 
                45.16 PB | .160 | 
| 15 | 5 | 2 | 1325 | Lalonde Gordon | 
 TTO                 | 
                45.20 | |
| 16 | 5 | 3 | 689 | Jonathan BORLÉE | 
 BEL                 | 
                45.23 | |
| 17 | 6 | 3 | 833 | Pavel MASLÁK | 
 CZE                 | 
                45.24 | |
| 18 | 7 | 1 | 1249 | Rafał Omelko | 
 POL                 | 
                45.37 | |
| 19 | 6 | 2 | 1055 | Brian GREGAN | 
 IRL                 | 
                45.42 | |
| 20 | 7 | 2 | 1426 | LaShawn Merritt | 
 USA                 | 
                45.52 | |
| 21 | 7 | 3 | 1324 | Machel CEDENIO | 
 TTO                 | 
                45.91 | |
| 22 | 8 | 2 | 1143 | Boniface Ontuga MWERESA | 
 KEN                 | 
                45.93 | |
| 23 | 8 | 3 | 1065 | Davide RE | 
 ITA                 | 
                45.95 | |
| 24 | 8 | 1 | 952 | Dwayne COWAN | 
 GBR                 | 
                45.96 | 
ms - Milliseconds - shown when two or more competitors finish with the same time down to hundredths of a second