The 27-year-old shot stopper is their first signing of the summer, as the Royals start a massive overhaul of their squad in preparation for the upcoming 2022/23 season.
Here we have a little deep-dive into Lumley's career so far and what he has to offer for the Royals.
Lumley has spent the majority of his career up to this point at Queens Park Rangers, coming through their academy. He had been out on loan at seven different clubs during his time at QPR, playing for the likes of Blackpool and Bristol Rovers.
He then joined current club Middlesbrough in July last year following the conclusion of his contract at QPR, signing a two-year deal. In his first season at the club, he made 34 appearances, keeping 13 clean sheets as Boro finished the season in seventh place, ending just five points off the play-offs.
Despite keeping 13 clean sheets last season for Boro as they narrowly missed out on the play-offs, Lumley's stats aren't the best, suggesting that the clean sheets were more because of the defence in front of him, rather than his own goalkeeping ability.
Out of the 31 goalkeepers in the Championship last season, Lumley came 24th in save percentage with 66.3% - which is lower than the current Reading goalkeeper, Luke Southwood.
What is more alarming about this stat is the aforementioned defence that Middlesbrough had during the last campaign. Boro finished seventh in the Championship and were one of the best teams in the division last season, especially in the second half of it.
This suggests that had Boro had a better keeper in between the sticks, then they may well have finished higher and earned themselves a play-off place and an opportunity to achieve promotion to the Premier League.