The 2020 Davis Cup World Group I was held on 5–6 March 2021 and 17–19 September 2021. The eight highest-ranked winners of the World Group I ties automatically progressed to the 2022 Davis Cup qualifying round. The four lowest-ranked winners took part in an additional knock-out tie in November 2021, the two winners progressing to the 2022 Davis Cup qualifying round and the two losers contesting the 2022 Davis Cup World Group I play-offs. The losing nations from the World Group I ties will compete in the 2022 Davis Cup World Group I play-offs.

Twenty-four teams participated in the World Group I, in a series decided on a home and away basis. The seedings are based on the nations ranking of 9 March.

These twenty-four teams were:

The eight highest-ranked (as at 20 September 2021) winners of the World Group I ties automatically progressed to the 2022 qualifiers. The four lowest-ranked winners took part in an additional knock-out tie in November 2021, with the two winners progressing to the 2022 qualifiers and two losers contesting the 2022 World Group I play-offs. The losing nations from the World Group I ties will compete in the World Group I play-offs in 2022.

#: Nations ranking as of 9 March 2020.