The 30-year-old German had driven for the team since their arrival in F1 at the start of 2010, and had a contract to race alongside Britain's Max Chilton this year.
But reports in Germany had suggested a split was imminent and a team statement on Monday morning confirmed a parting of the ways by mutual consent.
Team principal John Booth admitted the decision had been taken with financial considerations in mind, after the team narrowly missed out on 10th place in the constructors' championship last season.
He said: "Timo has made a very significant contribution to our team over the past three seasons, helping us to develop our package to the point where, for a large proportion of the 2012 season, we were holding 10th place in the constructors' championship.
"Timo is a fantastic driver and he has been a very popular member of the team.
"Our team was founded on the principle of benefiting from proven experience whilst also providing opportunities for young emerging talent to progress to the pinnacle of motorsport.
"Thus far, this philosophy has also been reflected in our commercial model. The ongoing challenges facing the industry mean that we have had to take steps to secure our long-term future.
"Tough economic conditions prevail and the commercial landscape is difficult for everyone, Formula One teams included.
"We would like to thank Timo for working with us to reach this decision, especially as he had a valid contract, and also for the contribution he has made to our team.
"We wish him all the best for his future and I would like to congratulate the next team acquiring the services of such a competitive, professional and experienced racer.
"We will provide an update regarding the completion of our driver line-up in due course."
Vitaly Petrov and Sebastien Buemi have already been touted as potential replacements for Glock, and would bring some helpful financial backing.
Glock's alternatives within F1 are slim, with the only other available seats for 2013 being at Caterham and Force India.
The former Jordan and Toyota driver said: "I have had three excellent years with the Marussia F1 Team, during which I had the chance to actively participate in building and developing the team in its endeavours to succeed within the Formula 1 World Championship.
"I would like to wish the team good luck in navigating this next period and thank everyone for the great times we shared and the support I have received.
"Although it is not the path I expected to be taking, I am in fact very excited about what the future holds in terms of my own career and I hope to comment on that very soon."