Under a new partnership between the two companies, their sales teams will sell ads across the combined network.
The network allows digital ads to be run for any length or frequency.
The two companies' sales teams are not merging and they will work under the direction of Avanti Screenmedia's sales director Jamie Ball and Streetbroadcast's managing director of sales, Mungo Knott.
Ball said the partnership harnesses the two companies' sales, marketing and creative experience to deliver what he claimed will be the largest out-of-home digital retail network in the UK.
Digital Life consists of more than 800 screens in shopping malls, retail and entertainment parks, city centres and high streets across the UK in 50 towns and cities, as well as 120 shopping locations.
It is understood that other out-of-home media owners wanting to join the network will be considered.
Knott said Digital Life delivers better "value communication" for clients and an "enhanced street experience" for the public.
He added that the alliance creates a nationwide digital retail offering "that advertisers have been waiting for".
Streetbroadcast employs 40 staff with a nine-strong sales team, while Avanti Screenmedia employs 35, of whom 10 work in sales.
Content from Trinity Mirror's Liverpool Echo is shown on Streetbroadcast's Liverpool screen. The other Streetbroadcast screens show BBC content, while Avanti screens show Sky content.
Streetbroadcast works on behalf of local authorities and commercial property owners to offer lamppost and six-sheet advertising.