| POS | Rank | Heat | BIB | ATHLETE | COUNTRY | RESULTS | ms* | 
|---|---|---|---|---|---|---|---|
| 1 | 1 | 3 | 3913 | Michael CHERRY |  USA | 44.82 Q | |
| 2 | 1 | 1 | 1270 | Isaac MAKWALA |  BOT | 44.86 Q | |
| 3 | 1 | 4 | 1551 | Anthony José ZAMBRANO |  COL | 44.87 Q | |
| 4 | 2 | 4 | 1097 | Steven SOLOMON |  AUS | 44.94 Q PB | |
| 5 | 1 | 6 | 3015 | Liemarvin BONEVACIA |  NED | 44.95 Q | |
| 6 | 2 | 3 | 1154 | Jonathan JONES |  BAR | 45.04 Q SB | |
| 7 | 1 | 5 | 1136 | Steven GARDINER |  BAH | 45.05 Q | |
| 8 | 2 | 1 | 2235 | Kirani JAMES |  GRN | 45.09 Q | |
| 9 | 2 | 5 | 3633 | Deon LENDORE |  TTO | 45.14 Q | |
| 10 | 1 | 2 | 2827 | Mazen Mawtan AL YASEN |  KSA | 45.16 Q PB | |
| 11 | 3 | 3 | 2634 | Christopher TAYLOR |  JAM | 45.20 Q | |
| 12 | 3 | 4 | 3438 | Wayde VAN NIEKERK |  RSA | 45.25 Q | |
| 13 | 4 | 4 | 1274 | Leungo SCOTCH |  BOT | 45.32 q | |
| 14 | 2 | 6 | 3958 | Michael NORMAN |  USA | 45.35 Q | |
| 15 | 2 | 2 | 1191 | Kévin BORLÉE |  BEL | 45.36 Q SB | |
| 16 | 3 | 1 | 1201 | Jonathan SACOOR |  BEL | 45.41 Q | .401 | 
| 17 | 4 | 3 | 3635 | Dwight ST. HILLAIRE |  TTO | 45.41 q | .404 | 
| 18 | 5 | 3 | 3468 | Luka JANEŽIČ |  SLO | 45.44 q SB | |
| 19 | 5 | 4 | 2437 | Davide RE |  ITA | 45.46 q SB | |
| 20 | 4 | 1 | 2583 | Demish GAYE |  JAM | 45.49 q | |
| 21 | 5 | 1 | 1137 | Alonzo RUSSELL |  BAH | 45.51 q SB | |
| 22 | 6 | 1 | 1076 | Alex BECK |  AUS | 45.54 PB | .538 | 
| 23 | 3 | 5 | 3019 | Jochem DOBBER |  NED | 45.54 Q | .540 | 
| 24 | 3 | 6 | 3625 | Machel CEDENIO |  TTO | 45.56 Q | |
| 25 | 3 | 2 | 3522 | Ricky PETRUCCIANI |  SUI | 45.64 Q | |
| 26 | 4 | 2 | 3964 | Randolph ROSS |  USA | 45.67 | |
| 27 | 4 | 6 | 2438 | Edoardo SCOTTI |  ITA | 45.71 | |
| 28 | 5 | 2 | 3427 | Zakithi NENE |  RSA | 45.74 | |
| 29 | 5 | 6 | 3428 | Thapelo PHORA |  RSA | 45.83 SB | |
| 30 | 6 | 6 | 2360 | Taha Hussein YASEEN |  IRQ | 46.00 SB | |
| 31 | 6 | 3 | 1453 | Gilles Anthony AFOUMBA |  CGO | 46.03 SB | |
| 32 | 7 | 3 | 1312 | Lucas CARVALHO |  BRA | 46.12 | .112 | 
| 33 | 4 | 5 | 2537 | Nathon ALLEN |  JAM | 46.12 | .114 | 
| 34 | 5 | 5 | 3497 | Sadam Suliman KOUMI EL NOUR |  SUD | 46.26 SB | |
| 35 | 6 | 5 | 2178 | Marvin SCHLEGEL |  GER | 46.39 | |
| 36 | 6 | 2 | 1546 | Jhon Alejandro PERLAZA |  COL | 46.55 | |
| 37 | 6 | 4 | 2719 | Julian Jrummi WALSH |  JPN | 46.57 | |
| 38 | 7 | 4 | 2953 | Jovan STOJOSKI |  MKD | 46.81 PB | |
| 39 | 7 | 1 | 3235 | Ricardo DOS SANTOS |  POR | 46.83 | |
| 40 | 7 | 2 | 1636 | Pavel MASLÁK |  CZE | 47.01 | |
| 41 | 7 | 5 | 2741 | Mikhail LITVIN |  KAZ | 47.15 | |
| 42 | 8 | 1 | 1454 | Bachir MAHAMAT |  CHA | 47.93 SB | |
| 43 | 7 | 6 | 1796 | Óscar HUSILLOS |  ESP | 48.05 | |
| 44 | 8 | 3 | 1148 | Mohammad Jahir RAYHAN |  BAN | 48.29 SB | |
| 45 | 8 | 6 | 2879 | Todisoa Franck RABEARISON |  MAD | 48.40 SB | |
| 46 | 8 | 2 | 4017 | Ahmed AL YAARI |  YEM | 48.53 SB | |
| 47 | 8 | 5 | 3212 | Karol ZALEWSKI |  POL | 2:15.38 | |
| 4 | 2780 | Emmanuel Kipkurui KORIR |  KEN | DQ | 
ms - Milliseconds - shown when two or more competitors finish with the same time down to hundredths of a second