The former Brentford man has signed a six-month loan deal with the Gers, who are aiming to win the Championship title in Scotland and gain automatic promotion to the Scottish Premiership at the end of the season.
Forrester is delighted to be joining Rangers and has also wished Doncaster the best of luck for the future.
Absolutely delighted to sign a deal with @RangersFC can't wait to put on the famous blue jersey thanks for all the welcoming messages— Harry Forrester (@harry_forrester) December 31, 2015
Also a goodbye and thank you to @drfc_official. Fans have been magnificent with me from day 1 ... wish you all the best in the future— Harry Forrester (@harry_forrester) December 31, 2015
Here is one for you my dad pulled out- me aged 6 pic.twitter.com/OhVN4n0O8F— Harry Forrester (@harry_forrester) December 31, 2015
Forrester has worked with current Rangers manager Mark Warburton at Watford and Brentford.
The attacking midfielder is a good player and has scored one goal in nine appearances so far this season.
The former Watford and Aston Villa prospect will be looking to establish himself in the Rangers first team in the coming weeks.
Rangers are at the top of the Scottish Championship table at the moment with 44 points from 18 matches, three points clear of Falkirk and Hibernian, who are currently second and third respectively in the standings.