Ross is already the fourth new player to join Casey Stoney's United ahead of the 2019/20 campaign following the existing arrivals of Jackie Groenen, Abbie McManus and Hayley Ladd.
The 29-year-old, who was most recently part of the Scotland squad at this summer's Women's World Cup, joined West Ham following their promotion to the WSL last year and finished her sole season with the Hammers by playing in the 2019 FA Cup final.
During her time at Manchester City, Ross was a WSL champion, a FA Cup winner and a Continental Cup winner. She has also played at club level in Sweden after earlier making her name as a prolific goalscorer at Scottish club Glasgow City.
Ross will bring a wealth of experience to an ambitious United squad aiming to continue the immense momentum of last season's Women's Championship title.
Fellow new arrival McManus, who is part of the England squad aiming to now finish third at the ongoing World Cup, will be one very familiar face for Ross, with the pair ex-City teammates.
United captain Alex Greenwood has also been part of England's squad this summer, while new signing Groenen has gone one better than the Lionesses with the Netherlands and will be playing in the World Cup final against the United States on Sunday.
Not only has the Dutch midfielder been a starter throughout the tournament, she actually scored the only goal of the semi-final against Sweden and was named Player of the Match.
Source : 90min