Media reports said that Barcelona would cover Rashford's wages this season after the player accepted a pay cut, with the option to buy.
The move came after Manchester-born Rashford, who made 426 senior appearances and scored 138 goals for United in all competitions, fell out of favour with manager Ruben Amorim, who called the 27-year-old's workrate into question.
"I'm very excited. It is a club where people's dreams come true, they win big prizes," Rashford said of his new club.
"What the club stands for means a lot for me. I feel like I am at home and a big factor in my choice to come here because it is a family place and a good place for good players to showcase their skills."
Rashford, who won two FA Cups, two League Cups and a Europa League title with United, ended last season on loan at EPL club Aston Villa where he netted two goals in 10 league games.
Meanwhile, Liverpool have signed French striker Hugo Ekitike from Eintracht Frankfurt for a reported stg 69 million ($A142 million).
Ekitike is Liverpool's second-most expensive recruit in the close season after the Premier League champions signed Germany midfielder Florian Wirtz for a club record stg 116 million ($A239 million).
Former Paris St Germain player Ekitike had a breakout campaign in 2024-25, scoring 15 Bundesliga goals in 33 appearances. He also struck four times as Frankfurt reached the quarter-finals of the Europa League.
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