Ronald Koeman's side beat Real Sociedad on penalties to advance to the final, while Athletic were surprise winners over Real Madrid, recording a 2-1 victory over the holders on Thursday.
Barca will enter Sunday's final as the favourites, and the Catalan outfit, as mentioned, will be bidding to lift the trophy for the 14th time in their history, reclaiming the crown from Real Madrid in the process.
Koeman's side were given a tough examination by Sociedad in Wednesday's semi-final but managed to triumph on penalties when the two teams could not be separated in normal play.
Barca are now on a run of nine games unbeaten in all competitions, while they have not lost a domestic match since the start of December, with things starting to turn for the club.
The Catalan giants still have a lot of work to do in La Liga if they are to be considered challengers for the title as they sit seven points off leaders Atletico Madrid, who have two games in hand.
Koeman will be determined to lift his first trophy as Barca boss this weekend, but Athletic, having ensured that there would not be another El Clasico, will enter the contest full of confidence.
Many expected Madrid and Barca to lock horns in Sunday's final, but Athletic had not read the script, with the Basque outfit triumphing courtesy of a 2-1 victory in Malaga.
The Lions have won the Spanish Super Cup on two previous occasions, the last of which came in 2015, when they incredibly beat Barca 5-1 on aggregate, including a 4-0 victory in the first leg at San Mames.
Athletic's last league match was actually against Koeman's side on January 6, and an entertaining match finished 3-2 to the Catalan outfit, with the result leaving Marcelino's side down in 12th position in the table.
The fact that Barca have had 24 hours more to prepare for this contest could make a huge difference, but Los Leones will have their eyes on a quickfire double over the two biggest clubs in Spain.
Barcelona Supercopa de Espana form: WLLWLW
Barcelona form (all competitions): WDWWWW
Athletic Bilbao Supercopa de Espana form: LLWDW
Athletic Bilbao form (all competitions): WDLWLW
Barca will again be without the services of Philippe Coutinho, Gerard Pique, Sergi Roberto and Ansu Fati through injury, but Lionel Messi could return from the hamstring issue that forced him to miss the semi-final.
Koeman is expected to resist the temptation to shuffle his pack on Sunday, meaning that Antoine Griezmann and Ousmane Dembele should retain their spots in attack, with Martin Braithwaite expected to be the player to drop out to allow Messi to return to the side.
It would not be a surprise to see Marcelino select the same XI that took to the field against Madrid, with Inaki Williams joining Raul Garcia in the final third, where there should also be spots for Iker Muniain and Oscar de Marcos in the wide positions.
Barcelona possible starting lineup:
Ter Stegen; Dest, Araujo, Lenglet, Alba; Busquets, De Jong; Griezmann, Pedri, Dembele; Messi
Athletic Bilbao possible starting lineup:
Simon; Capa, Nunez, Martinez, Balenziaga; De Marcos, Vencedor, D Garcia, Muniain; Williams, R Garcia
We say: Barcelona 2-1 Athletic Bilbao
Barca will be the favourites to triumph on Sunday night, and we are expecting Koeman's side to lift the trophy. Messi's likely return will be a huge boost for the Catalan giants, and we are predicting a narrow win for Barca as tiredness could be an issue for Athletic due to the relatively fast turnaround.