Guy was the son of Colonel Joseph Robert Wethered, C.M.G., D.S.O., and his wife, Dorothy Kathleen Amy Fitzgerald of The White House, Marlow, Buckinghamshire. He was born in Edinburgh and had a sister.

He was educated at Radley and Matriculated in 1938. He was up at Christ Church for one year in which he was a Member of the University Athletics team.

He was remembered in The Annual Report of the Achilles Club:

“He, quickly, established a reputation as the most promising half miler of his generation, with real world class potential. In his freshman year after placing second in the Varsity Match 880y of 1939 to J O Moreton, he then won for Oxford and Cambridge against Harvard & Yale (15 July 1939, White City) in 1:52.4, breaking double Olympic Champion Douglas Lowe's match record in the process.

He was elected Hon Sec of OUAC for 1940, and would in the normal course of events have gone on to be President in 1941. But war intervened.”

Sir John Moreton wrote in appreciation of the tribute  “We were colleagues in the winning OUAC team against Cambridge in 1939. For the match against Harvard & Yale in July I was chosen as first string in the 880 yards, based on form up to that point. I have vivid memories of the race, because on entering the home straight in the lead I felt I had the race in hand, and was more than surprised when Guy shot past me to establish a new match record. From that point on it was obvious he was heading for a glittering future.

“I remember Guy as a charming and modest companion. I learnt of his death with great sadness while serving myself also on the Burma front.”

He was gazetted to the Gloucestershire Regiment with which his father had served. His father had died in January 1942.

The undermentioned from R.A.C. to be War Subs.Capts., 1st Apr. 1943, retaining their present seniority: —
War Subs. Capts.: —  A. C. Steadman (120931). G. E. F. Wethered (134368).
A. W. G. Hadingham  134302).

He died of wounds on 22 November 1944 at Pinwe having been injured whilst trying to help some wounded men back.

He is buried in Taukkyan War Cemetery Plot 6. H. 16.

He is commemorated on the Lords Roll of Honour and at the Royal Memorial Chapel Sandhurst.

His sister’s husband, Captain James Makepeace Thackeray Ritchie of the Oxfordshire & Buckinghamshire Light Infantry had been killed in May 1940.

From the War Diary of the 10th Gloucesters at Pinwe
15th-26th November 1944
 by Major R.S. Butler.

19th November - orders came to prepare to carry out a frontal attack to capture the Gyobin Chaung and Pinwe railway station. Two British field artillery regiments put down a barrage and an air strike was arranged for the Gyobin Chaung area.

21st November - patrols sent out and Battalion moved up to its assembly area. The enemy positions could not be located due to the thick jungle. 

22nd November - After a short bombardment the Battalion advanced at 1000 hrs. "D" Coy. reached the Gyobin Chaung, dealing with the enemy positions they encountered. "C" Coy. came under heavy fire from a well concealed machine gun post that was protected by a ring of snipers. "C" Coy. dug in, Major MacLaurin was wounded during this advance. Capt. O.M. Schryver, crawled out to rescue a wounded man, but was killed in the attempt.
"A" Coy. ran into an enemy bunker position, which was dealt with by a 2 platoon attack. After crossing the Chaung they ran into heavy machine gun and mortar fire. They beat off an enemy attack but all the company's officers were killed (including OC, Major  G.E.F Wethered wounded. "B" Coy. followed up and found more of the enemy moving into position on the Chaung behind "A" Coy. They fought off an attack and dug in, but were suffering from snipers hidden in the trees; Major A.C. Steadman (OC "B" Coy.) and his 2 subalterns were killed.