Norwich were first to ensure their place earlier this month, with the Hornets following them after a 1-0 victory over Millwall on Saturday, and two games remain in the title race.
Along with those to enjoy automatic promotion, the four clubs to meet in the playoffs have now been finalised, with a third spot in the Premier League up for grabs.
The final day of the regular Championship season is May 8, and with the playoff final to be held at Wembley on May 29, the two-legged semi-finals will be held between those dates.
As it stands, Brentford are third and hold a game in hand – which will be played on Tuesday night against Rotherham – and would therefore play Barnsley.
Bournemouth and Swansea, the two clubs with the most recent top-flight experience, are fourth and fifth and would therefore be pitted against each other if all stays the same.
Ivan Toney, Brentford‘s No. 17, is the Championship’s leading scorer this season with 29 goals, and only Reds loanees Harvey Elliott and Harry Wilson (both 11) and Norwich‘s Emi Buenda (16) have produced more assists than the striker (10).