The 2021 Biella Challenger Indoor III was a professional tennis tournament played on hard courts. It was the 3rd edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Biella, Italy between 8 and 14 March 2021.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Australia | James Duckworth | 102 | 1 | |
 Italy | Andreas Seppi | 107 | 2 | |
 Japan | Yūichi Sugita | 108 | 3 | |
| Japan | Yasutaka Uchiyama | 109 | 4 | |
| Peter Gojowczyk | 125 | 5 | ||
 Austria | Jurij Rodionov | 139 | 6 | |
| Marc-Andrea Hüsler | 149 | 7 | ||
 Slovakia | Martin Kližan | 156 | 8 |
The following players received wildcards into the singles main draw:
The following player received entry into the singles main draw using a protected ranking:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
See main article: 2021 Biella Challenger Indoor III – Singles.
Andreas Seppi def. 
Liam Broady 6–2, 6–1.See main article: 2021 Biella Challenger Indoor III – Doubles.
Quentin Halys / Tristan Lamasine def. 
Denys Molchanov / Sergiy Stakhovsky 6–1, 2–0 ret.