Newcastle had already announced fixtures against Burton Albion, York City and Harrogate Town.
Steve Bruce’s Premier League squad is being split for the York and Harrogate games, which will both be staged on Sunday, July 18. The Burton game is on Friday, July 30 (7.45pm).
United have played once before at Rotherham’s 12,201-capacity home. A goal from Christian Atsu gave the club a 1-0 win in the Championship in the 2016/17 season during Rafa Benitez’s time as manager.
Rotherham signed midfielder Dan Barlaser from Newcastle last summer. The club was relegated from the Championship on the final day of last season.
Meanwhile, Newcastle are yet to confirm plans for a pre-season training camp next month.
A training camp in Portugal has been mooted as an option by Bruce, but the foreign travel is complicated by coronavirus travel and quarantine restrictions, and the club, which spent a week training in York last year, may again stay on home soil given that Portugal is no longer on the Government’s “green list” of countries.
Speaking to BBC Radio Newcastle last month, head coach Bruce said: “I would think if we went away, there wouldn’t be any games – it wouldn’t be wise to play games, and have people travelling. We’re looking at a couple of camps – one in this country, and one in Portugal.”