The Warriors/Hawks partnership player, who can play across the back line and has represented Scotland Sevens, is looking forward to make an impact in the Championship.
"I'm excited to be signing for London Scottish. It is a good change up for me and I cannot wait to get stuck into some Championship games this season," said Beattie.
London Scottish Director of Ruby Dave Morris is happy to add Beattie to his backline options.
"We are delighted to welcome Bobby to London Scottish. He is a very adaptable player covering a range of positions with an excellent skill set. We currently have seven backs out injured so Bobby will get an immediate opportunity to pull on the famous London Scottish jersey. Bobby has some strong friendships with current Scottish players from their time together at Glasgow Warriors which is hugely beneficial when joining mid-season."
Joining Beattie in coming south of the border is flanker Lewis Wynne who was a near ever-present with the Scots in the early part of the season until he was recalled by the Scottish Rugby Union to play for Edinburgh in the Guinness PRO14. Wynne was named on the bench for two games and started a game against Muster, whilst back up in Scotland. He now resumes his season long loan from Glasgow Warriors.
Both Beattie and Wynne go into contention for selection this weekend as we conclude the group stages of The Championship Cup against Jersey Reds.