Tony Curran played Priest in Blade II (2002), Man in Black Agent in X-Men: First Class (2011), Bor Burison in Thor: The Dark World (2013 MCU film), and Finn Cooley in Marvel's Daredevil (2015 MCU TV series) S02E04 "Penny and Dime".
Leonor Varela played Nyssa in Blade II (2002) and Camilla Reyes in Agents of S.H.I.E.L.D. (2013) S01E02 "0-8-4".
Bruce Campbell played different cameo roles in Sam Raimi’s Spider-Man trilogy: Ring Announcer in Spider-Man (2002), Snooty Usher in Spider-Man 2 (2004), and Maître d’ in Spider-Man 3 (2007). He also voiced the Tutorial Guide in the video games based on the same films, as well as the Xtreme Reporter in The Amazing Spider-Man (2012 video game). He played Pizza Poppa in Doctor Strange in the Multiverse of Madness (2022), an MCU film also directed by Sam Raimi.
Jon Favreau played Franklin "Foggy" Nelson in Daredevil (2003) and then Happy Hogan in Iron Man (2008 MCU film) and reprised the role in subsequent MCU films featuring the character.
Patton Oswalt played Hedges in Blade: Trinity (2004), the five Koenig brothers in Agents of S.H.I.E.L.D. (2013), as well as Pip the Troll in Eternals (2021 MCU film). He also voiced M.O.D.O.K. in Marvel's M.O.D.O.K. (2021 stop-motion animated TV series).
Ryan Reynolds played Hannibal King in Blade: Trinity (2004), Wade Wilson / Deadpool in X-Men Origins: Wolverine (2009), Deadpool (2016) and Deadpool 2 (2018). He will reprise the role of Deadpool in Deadpool 3, which is an MCU film.
Laurence Fishburne voiced the Silver Surfer in Fantastic Four: Rise of the Silver Surfer (2007), played Bill Foster in Ant-Man and the Wasp (2018 MCU film), and voiced the Beyonder in Marvel's Moon Girl and Devil Dinosaur (2023).
Tim Blake Nelson played Samuel Sterns in The Incredible Hulk (2008 MCU film) and Dr. Harvey Allen in Fantastic Four (2015). He will reprise his role as Samuel Sterns / the Leader in Captain America: Brave New World (2024 MCU film).
Clancy Brown voiced Mr. Sinister in Wolverine and the X-Men: Foresight (2009), voiced Taskmaster in Iron Man & Captain America: Heroes United (2014), played Ray Schoonover / "the Blacksmith" in Marvel's Daredevil (2015 MCU TV series), and voiced Surtur in Thor: Ragnarok (2017).
Djimon Hounsou voiced Black Panther in Black Panther (2010 animated TV series) AKA Black Panther: Who is the Black Panther? He then played Korath in Guardians of the Galaxy (2014) and Captain Marvel (2019), which are MCU films.
Olivia Munn played Chess Roberts in Iron Man 2 (2010 MCU film) and Betsy Braddock / Psylocke in X-Men: Apocalypse (2016).
Idris Elba first played Heimdall in Thor (2011) and reprised this role in subsequent MCU films featuring the character. He also played Moreau in Ghost Rider: Spirit of Vengeance (2011).
Colm Feore played Laufey in Thor (2011 MCU film) and Donald Menken in The Amazing Spider-Man 2 (2014).
Hiroyuki Sanada played Shingen Yashida in The Wolverine (2013) and Akihiko (Yakuza boss executed by Hawkeye) in Avengers: Endgame (2019 MCU film). Archive footage of Hiroyuki Sanada from Avengers: Endgame was used in Hawkeye (2021) S01E01 "Never Meet Your Heroes".
Elena Satine played Lorelei in Agents of S.H.I.E.L.D. (2013 MCU TV series) and then Sonya Simonson / Dreamer in The Gifted (2017).
Aaron Taylor-Johnson played Pietro Maximoff / Quicksilver in Captain America: The Winter Soldier (2014) and Avengers: Age of Ultron (2015), which are MCU films. He will play Sergei Kravinoff / Kraven the Hunter in Kraven the Hunter (2023 Sony's Spider-Man Universe film).
Evan Peters played Peter Maximoff / Quicksilver in X-Men: Days of Future Past (2014), X-Men: Apocalypse (2016), Deadpool 2 (2018), and Dark Phoenix (2019). He also played Ralph Bohner / "Pietro Maximoff" in WandaVision (2021), an MCU TV series.
Josh Brolin played Thanos in Guardians of the Galaxy (2014 MCU film) and reprised his role in subsequent MCU works featuring the character. He also played Nathan Summers / Cable in Deadpool 2 (2018 Fox X-Men universe film).
Michael B. Jordan played Johnny Storm / Human Torch in Fantastic Four (2015), and then played Erik Stevens / N'Jadaka / Killlmonger in Black Panther (2018 MCU film).
Donald Glover voiced Miles Morales / Spider-Man in Season 3 of the Ultimate Spider-Man animated TV series. He played Aaron Davis / Prowler in Spider-Man: Homecoming (2017 MCU film). He had a cameo appearance as a variant of Prowler in Spider-Man: Across the Spider-Verse (2023).
Hayley Lovitt played a young Janet van Dyne / The Wasp in Ant-Man (2015) and Ant-Man and the Wasp (2018), which are both MCU films. She also played Sage in The Gifted (2017).
Karan Soni played Dopinder in Deadpool (2016) and Deadpool 2 (2018) which are both Fox X-Men universe films. He voiced Pavitr Prabhakar / Spider-Man India in Spider-Man: Across the Spider-Verse (2023). He will reprise the role of Dopinder in Deadpool 3, which is an MCU film.
Source: Karan Soni and Leslie Uggams Returning for 'Deadpool 3'. Collider
Oscar Isaac played Apocalypse in X-Men: Apocalypse (2016 Fox X-Men universe film), Marc Spector / Steven Grant / Jake Lockley / Moon Knight in Moon Knight (2022 MCU TV series), and voiced Miguel O'Hara / Spider-Man 2099 in Spider-Man: Across the Spider-Verse (2023).
Mahershala Ali played Cornell Stokes / Cottonmouth in Marvel's Luke Cage (2016 MCU TV series) on Netflix. He voiced Aaron Davis / Prowler in Spider-Man: Into the Spider-Verse (2018). He made a voice cameo as Blade in Eternals (2021 MCU film). He is set to play Blade in a 2024 Blade film.
Aubrey Plaza played Lenny Busker in Legion (2017 TV series), and will play a to-be-confirmed character in Agatha: Coven of Chaos (an MCU TV series to be released in 2023 or 2024).
Source: ‘WandaVision’ Spinoff ‘Agatha: Coven of Chaos’ Casts Aubrey Plaza. Variety
Daniel Kaluuya played W'Kabi in Black Panther (2018 MCU film) and voiced Hobart "Hobie" Brown / Spider-Punk in Spider-Man: Across the Spider-Verse (2023).
Kathryn Hahn voiced Olivia Octavius / Doctor Octopus in Spider-Man: Into the Spider-Verse (2018) and then played Agatha Harkness / Agnes in WandaVision (2021 MCU TV series). She will reprise her role as Agatha Harkness in the upcoming MCU TV series, Agatha: Coven of Chaos (an MCU TV series to be released in 2023 or 2024).
Hailee Steinfeld voiced Gwen Stacy / Spider-Woman / Spider-Gwen in Spider-Man: Into the Spider-Verse (2018) and then played Kate Bishop in Hawkeye (2021 MCU TV series). She reprised her role as Gwen Stacy / Spider-Woman in Spider-Man: Across the Spider-Verse (2023).
Brian Tyree Henry voiced Jefferson Davis in Spider-Man: Into the Spider-Verse (2018) and reprised his role in subsequent Spider-Verse films featuring the character. He portrayed Phastos / Phil Stoss in The Eternals (2021), an MCU film.
Lake Bell voiced Vanessa Fisk in Spider-Man: Into the Spider-Verse (2018), Natasha Romanoff / Black Widow in Season 1 of What If...? (2021 MCU TV series), and then played Dr. Graham in Black Panther: Wakanda Forever (2022 MCU film).
Russell Crowe played Zeus in Thor: Love and Thunder (2022 MCU film), and will play the father of Sergei Kravinoff / Kraven the Hunter in Kraven the Hunter (2023 Sony's Spider-Man Universe film).
Note: To keep the list short, I am only including actors who have played live-action Marvel characters. This excludes voice actors who have voiced multiple Marvel characters but have not played any in live-action.