The Gunners welcome the Canaries to North London seeking to get off the mark for the Premier League season and are at risk of losing their first four top-flight games for the first time since the 1923-24 season.
Ramsdale's only appearance for the Gunners so far came in their 6-0 EFL Cup thrashing of West Bromwich Albion, whereas Tomiyasu only arrived at the club on deadline day from Bologna.
However, both players will be making their Premier League debuts for the club on Saturday, while Ben White and Gabriel Magalhaes return to form the centre-back pairing.
Ainsley Maitland-Niles has been handed the nod in midfield over Thomas Partey - who makes the bench - and Albert Sambi Lokonga will partner the Englishman against the Canaries.
Emile Smith Rowe has overcome a bout of illness to make the bench, while Pierre-Emerick Aubameyang and Nicolas Pepe both start.