The London-listed hospitality firm revealed that total sales dived by 57 per cent to £459.8m in 2020 after its sites were forced to close their doors for large periods.
The plunge in sales and pandemic costs caused it to plummet to a £127.6m pre-tax loss for the year, compared to a £37.3m loss in 2019.
It added that its short-term outlook remains "uncertain" while lockdown restrictions remain in place.
TRG undertook a major restructuring during the pandemic, closing around 250 of its leisure and concessions sites – in a move that largely hit its Frankie & Benny's, Chiquito and Food & Fuel brands.
The company, which now has around 400 sites, said its planned capital raise will be the "last step" in its restructuring plan as it prepares to rebound once restrictions lift.
It also told investors that it is in a "strong" position to deliver an accelerated reopening plan as measures ease and is "well-positioned" to benefit over the long term.
Andy Hornby, chief executive of TRG, said: "The Covid-19 pandemic has presented enormous challenges for our sector, but the TRG team has responded decisively to restructure our business whilst preserving the maximum number of long-term roles for our colleagues.
"TRG is operationally a much stronger business than 12 months ago. The capital raise announced today, alongside the debt refinancing announced last week, represents the last important step in our restructuring process, and provides TRG with the long-term flexibility to invest in growing our business.
"Whilst the sector outlook remains uncertain, and we are mindful of continuing restrictions across the UK, we are confident that the actions announced today will allow us to emerge as one of the long-term winners."
Harry Barnick, senior analyst at Third Bridge, said the results beat some estimates. He added that the group is unlikely to be able to open all of its Wagamama Frankie & Benny’s and Garfunkel’s restaurants from mid-April due to its limited scope for outdoor seating. “Instead, its pub operations will have to lead the charge in the hope that its restaurants catch up over the summer months.
"Whilst demand is expected to recover strongly over the summer months, The Restaurant Group is still in hot water. Its bias towards urban restaurant locations is just where sales are likely to be weakest. Where demand will settle after the initial rush in bookings also poses a risk, especially with the furlough programme set to finish in September."
Also commenting was Susannah Streeter, senior investment and markets analyst, Hargreaves Lansdown. “There may now be a roadmap to reopening for the hospitality sector, but it’s not come soon enough for Restaurant Group,” she said.
"Pent-up demand from diners appears to be there, but it will take time to be unleashed. The cash injection from this latest rights issue will give [the company] some breathing space, but there may well be more restructuring pain to come, as a slimmed-down version of [TRG] emerges from the crisis.’’