Ferris left the Kerry training panel after the Munster final that year (in which he was unable to play), owing to poor health and Garda Special Branch surveillance.

[5] He was arrested by Gardaí in Youghal, County Cork, on 14 February 1975, along with two other IRA members, viz., Danny O'Sullivan and Robert McNamara.

Ferris was not convicted of robbery but was remanded to Portlaoise Prison pending further charges of membership in the IRA as a proscribed organisation.

[8] He was arrested again in February 1976 at a Garda roadblock in Ballinrobe, County Mayo after attending the funeral of Frank Stagg.

[11] In September 1984, Ferris attempted to import seven tons of explosives, firearms and ammunition,[12] as well as medications, training manuals, and communications equipment, using the fishing vessel Marita Ann, which was piloted by Mike Browne, another IRA member.

[13] The plan involved rendezvousing with the trawler Valhalla, captained by Bob Anderson, which sailed from Boston, Massachusetts, transferring arms and ammunition to the Marita Ann and sailing to the south coast of County Kerry, where a number of cars were on standby to deliver the weapons to various Provisional IRA arms dumps.

On 11 December 1984, Ferris and two other members of the Marita Ann crew, including Browne and a United States citizen, John Crawley, were sentenced to ten years imprisonment at Portlaoise Prison.

In February 2005, the Minister for Justice, Equality and Law Reform, Michael McDowell, using parliamentary privilege, named Ferris—as well as Gerry Adams and Martin McGuinness—as a member of the IRA Army Council, an allegation that has been denied by Ferris and the Sinn Féin leadership.

In July of that year, the Irish Independent reported that Ferris,[16] along with Adams and McGuinness, had stepped down from the Army Council in the lead-up to an IRA statement on its future.

Ferris has courted controversy by his refusal to condemn the murder of Detective Garda Jerry McCabe during a botched Post Office raid by the Provisional IRA in 1996.

Ferris had also greeted Pearse McAuley and Kevin Walsh, the men charged with the manslaughter of Garda McCabe, upon their release from prison as part of the Good Friday Agreement.

At the 2017 Sinn Féin Ard Fheis, Gerry Adams confirmed neither he nor Ferris would be standing at the 2020 Irish general election.