Featherstone say under the terms of the agreement Wakefield will not be able to recall Walker, who is out of contract at the end of the year.
Rovers football manager Ian Hardman said: “’Alex is an exciting player that will fit into the squad well and add options to our backline.
“He also has the benefit of experience in helping London Broncos gain promotion through the play-offs, a feat we hope to emulate later this year.”
Walker joins side Featherstone having made 10 appearances for Trinity and is set to make his debut at Batley on Sunday.
Walker said: “I’m excited and really looking forward to getting started with the boys.
“I’m fortunate to have had the experience of gaining promotion to Super League with London Broncos and hope that experience can help get Fev to Super League this year.”
Walker joins Featherstone who are aiming for promotion into Super League this season. James Webster’s side have won 13 from their 14 games this season, sitting just behind leaders Toulouse in the table.
Rovers lost their first game of 2021 on Sunday as they fell to a 23-6 defeat against French side Toulouse. There were more than 3,000 in attendance to witness the top of the table clash at the Millennium Stadium.
Walker has won six caps for Scotland since making his international debut in 2015 and he will be hoping to represent the Bravehearts in his second World Cup this autumn.
Scotland have been drawn in a group with Australia, Fiji and Italy at this year’s World Cup. However, the tournament hangs in the balance after Australia and New Zealand’s decision to withdraw from the World Cup.
The Harlow-born full-back scored 41 tries in 102 games for London Broncos between 2014-19.