The 23-year-old arrives on a free transfer following his release from boyhood club earlier in the summer.
The central midfielder has signed a two-year deal with the Seasiders with the option to extend by a further 12 months.
“I’m delighted to be joining Blackpool and I can’t wait to get started,” Robson said.
“It wasn’t an easy decision to leave Sunderland, which is where I’ve grown up and developed over the years.
“But after speaking to Neil Critchley and hearing what he had to say about the team and where he wants to take it, I felt it was a journey I wanted to be a part of.
“Blackpool is on the up and I’m looking forward to seeing what the future brings here.”
The free agent, who scored one goal in 14 appearances for the Black Cats, impressed during loan spells with Dundee and Grimsby Town.
The central midfielder joined his local side at the age of eight and rose through the ranks before turning professional in 2014.
His departure this summer brought an end to his 16-year spell with the Wearside outfit.
It’s understood Blackpool saw off competition from a host of other clubs, with Blackpool’s League One rivals Fleetwood Town, Portsmouth, Ipswich Town and Oxford United all being linked with the midfielder.
“I’m excited to welcome Ethan to Blackpool and I am really looking forward to working with him,” head coach Neil Critchley said.
“He’s a highly rated, athletic midfielder who I have been aware of for a number of years and watched him develop at Sunderland.
“I believe he will be a valuable asset to the team, and he fits the profile well of the type of player we want to bring to the club.”
Robson joins Keshi Anderson, Marvin Ekpiteta, CJ Hamilton, Oliver Sarkic and Jerry Yates in signing for the Seasiders this summer.