Swansea finished sixth in the regular season, while Brentford missed the chance to secure automatic promotion on the final day.
Swansea City's comfortbable 4-1 victory over Reading on the final day of the season saw them pip Nottingham Forest to the final playoff spot in dramatic fashion.
The Swans now have a fantastic opportunity to make their return to the big time following a two-year absence, although Swansea had Forest's capitulation to thank for their playoff berth more than anything else.
Only one goal separated Swansea and Forest in the table after 46 matches, with the latter's catastrophic 4-1 defeat to Stoke City paving the way for Steve Cooper's side to break into the top six and set up a semi-final clash with Brentford.
Swansea gained promotion to the Premier League for the first time via the playoff route in 2011, as they overcame Forest in the semi-finals before defeating Reading 4-2 in the final at Wembley Stadium.
Of course, Cooper's men must defeat Brentford over two legs before they can think about stepping out onto the Wembley turf, but the last time Swansea made an appearance at the home of English football, they ultimately travelled back to Wales with the League Cup in tow after a 5-0 drubbing of Bradford City in 2013.
Meanwhile, Brentford have a magnificent chance to secure a route into the Premier League for the first time ever, but the final day of the Championship season was nothing less than a bitter disappointment for Thomas Frank and his players.
The Bees had a simple task - defeat lowly Barnsley and hope that Queens Park Rangers pull off a result against West Bromwich Albion - and Brentford would be guaranteed Premier League football next season.
QPR did their bit as they held West Brom to a 2-2 draw, but Brentford suffered the same fate for the second game in succession as Clarke Oduor bagged an injury-time winner for Barnsley at Griffin Park, keeping the Tykes up in the process.
Frank's men also succumbed to a 1-0 defeat to Stoke in their penultimate game of the season, and it may seem inconceivable to some fans as to how Brentford have been forced to settle for a spot in the playoffs.
The Bees enjoyed an eight-game winning streak prior to the loss to Stoke and notched up 80 goals throughout the campaign - 25 of those for Ollie Watkins, who just missed out on the Golden Boot by one goal to Fulham's Aleksandar Mitrovic.
There is no time for Brentford to dwell on those two agonising defeats, however, as the final promotion spot is still very much up for grabs heading into August.
Swansea Championship form: WWLDWW
Brentford Championship form: WWWWLL
With regards to Brentford, Nikos Karelis is the only injury concern for Frank, who otherwise has a fully-fit squad at his disposal for the first leg of the playoff semi-final.
Mathias Jensen will be hoping to come back into the middle of the park, but Frank is unlikely to make too many alterations to his side despite a disappointing previous two results.
Swansea possible starting lineup:
Mulder; Hoorn, Cabango, Guehi; Roberts, Grimes, Fulton, Routledge; Gallagher; Ayew, Brewster
Brentford possible starting lineup:
Martin; Dalsgaard, Jansson, Pinnock, Henry; Jensen, Norgaard, Dasilva; Mbuemo, Watkins, Benrahma
We say: Swansea City 1-1 Brentford
There is no denying the attacking talent in Brentford's ranks despite their final-day disappointment, but the clash with a jubilant Swansea, on paper, represents a much more challenging fixture than Stoke or Barnsley do. The Swans have every reason to be optimistic heading into the first leg, but we expect the two sides to share the spoils and leave everything to play for in next Wednesday's second leg at Griffin Park.